Patterns of Failure in Head and Neck Cancer Post Chemo Radiation

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RxDrug of choiceCisplatin (sensitizer) or Pembrolizumab (salvage immunotherapy)

AltAlternativesCetuximab, Nivolumab, Docetaxel

⊘AvoidNon-curative re-irradiation in patients with prior severe late toxicity (e.g., grade 3-4 necrosis).

DxTest of choice3-month post-treatment PET/CT

ScKey scoreTNM Staging (8th Ed) and p16 status

→When to referAny suspected recurrence or persistent disease at 3 months post-CRT

In-field failure is the dominant pattern of recurrence; surgical salvage with R0 margins offers the best chance for survival, especially in HPV-positive disease.

Treatment failure following definitive chemoradiotherapy (CRT) for head and neck squamous cell carcinoma (HNSCC) occurs in approximately 21.8% of patients, representing a critical challenge in organ-preservation strategies. These failures are categorized spatially as in-field (within the high-dose volume), marginal (at the field edge), or out-of-field, and temporally as persistent or recurrent disease. While HPV-positive status confers a significant survival advantage after failure, p16-negative disease often presents with aggressive marginal recurrences and early distant metastasis. Management requires a multidisciplinary approach, prioritizing surgical salvage when resectable, as negative margins (R0) reduce local failure risk by over 50%. Emerging strategies like adaptive radiotherapy and delta-radiomics aim to identify biological resistance early, allowing for real-time treatment modification to improve locoregional control.

Overview and Recommendations

Background

•Treatment failure in HNSCC post-CRT encompasses locoregional failure (LRF), distant metastasis (DM), and organ function preservation failure (OFPF), the latter occurring in over 20% of patients due to chronic feeding tube or tracheostomy dependence.
•Spatial classification is the primary technical metric for failure analysis, distinguishing between in-field (>95% of recurrence within the 95% isodose), marginal (20-95% within the volume), and out-of-field (<20% within the volume) recurrences.
•HPV/p16 status serves as the most powerful prognosticator of survival after failure, with p16-positive patients surviving nearly 2 years longer post-progression (median OS 2.6 years) compared to p16-negative counterparts (median OS 0.8 years).
•Biological radioresistance is frequently driven by tumor hypoxia, where a baseline tumor-to-muscle ratio (TMR) ≥ 1.6 correlates with a nearly six-fold increase in locoregional failure risk (HR 5.8).
•Institutional volume significantly impacts outcomes, as patients treated at low-accruing centers face a 72% to 91% increased risk of mortality compared to those at high-volume academic centers, independent of radiotherapy protocol compliance.

Evaluation

•Suspect treatment failure in patients presenting with new-onset pain, enlarging neck masses, unexplained weight loss, or worsening dysphagia following the completion of CRT.
•Perform a comprehensive fiberoptic endoscopic examination of the upper aerodigestive tract at every post-treatment visit to identify mucosal recurrence or persistent ulceration.
•Order a scan at approximately 3 months post-treatment as the gold-standard baseline; a negative 3-month scan has a high negative predictive value and significantly reduces the utility of subsequent routine PET surveillance.
•Utilize rigid or deformable image registration to map the recurrent tumor volume back to the original planning CT to determine if the failure was in-field (suggesting radioresistance) or marginal (suggesting a geographic miss).
•Assess for distant metastasis, particularly in patients with T4 disease or pN2-3 nodal status, as these groups have a 2-year distant progression rate reaching 76-78%.
•Evaluate for late-onset treatment complications that mimic failure, such as carotid stenosis, osteoradionecrosis (ORN), or pharyngoesophageal junction (POJ) stenosis requiring endoscopic dilatation.
•Monitor thyroid function (TSH/Free T4) regularly, especially if the thyroid volume receiving 45 Gy (V45) exceeded 67% during treatment.
•Consider biopsy of any PET-avid or clinically suspicious lesion, though clinicians must be wary of post-radiation necrosis which can yield false positives on functional imaging.

Management

•Prioritize surgical salvage for resectable locoregional recurrences, as it remains the only curative-intent option for most patients.
•Aim for R0 resection (negative margins) during salvage surgery, which reduces the risk of subsequent local failure by approximately 51% (HR 0.49).
•Utilize (TORS) for early-stage (T1-T2) oropharyngeal recurrences to achieve a 2-year OS of ~68% while minimizing long-term gastrostomy dependence.
•Consider supracricoid partial laryngectomy (SCPL) for qualifying laryngeal recurrences to achieve high disease-specific survival (up to 100% in select series) while avoiding total laryngectomy.
•Initiate systemic chemoimmunotherapy for unresectable or widely metastatic disease; regimens may include or with or without platinum-based chemotherapy.
•Administer re-irradiation (re-RT) cautiously in patients unfit for surgery, often using highly conformal techniques like or to a dose of 60-70 Gy if the cumulative dose to organs at risk allows.
•Integrate hyperthermia with re-irradiation for unresectable recurrences to potentially improve overall response rates (ORR) to over 80%.
•Manage oligometastatic disease (≤5 lesions) with a combination of systemic therapy and local ablative radiotherapy to improve progression-free survival from 7.7 to 13 months.
•Maintain a minimum point dose (Dmin) of at least 54 Gy to the primary tumor volume in any re-treatment of nasopharyngeal carcinoma to maximize local control.
•Refer patients to high-volume tertiary centers for salvage interventions, given the high complexity and multidisciplinary requirements of recurrent head and neck cancer management.

Board Review — High Yield

•In-field Failure, Recurrence within the high-dose volume (>95% of Vrecur), typically indicating biological radioresistance.
•Marginal Miss, Recurrence at the edge of the radiation field (20-95% of Vrecur), often due to inadequate target delineation.
•HPV/p16 Status, The strongest predictor of survival after failure; p16+ patients have significantly better salvage outcomes.
•3-Month PET/CT, The optimal timing for post-treatment response assessment; earlier scans have high false-positive rates due to inflammation.
•R0 Resection, Negative surgical margins in the salvage setting reduce local failure risk by ~50%.
•Hypoxia (FAZA PET), TMR ≥ 1.6 is a biomarker for radioresistance and a 6-fold increase in LRF risk.
•Dmin 54 Gy, Minimum point dose threshold required for local control in advanced nasopharyngeal carcinoma.
•Delta-Radiomics, Analysis of imaging feature changes during treatment (e.g., at week 4) that predicts late toxicity and failure better than baseline scans.

Deep Dive — Evidence Details

Introduction and Definitions of Failure

▸Treatment failure is categorized into locoregional recurrence, distant metastasis, and functional failure (OFPF).
▸In-field recurrence is the most frequent spatial pattern, accounting for over 50% of local failures in some HNSCC subtypes.
▸T4 tumor stage and smoking are independent predictors of failing to achieve successful organ preservation.

HY High Yield: Functional failure (feeding tube or tracheostomy dependence) is considered a treatment failure even in the absence of cancer, as the primary goal of CRT is functional organ preservation [20].

Treatment failure following definitive chemoradiotherapy (CRT) for head and neck squamous cell carcinoma (HNSCC) represents the inability of the primary therapy to achieve or maintain a disease-free state. While CRT aims for organ preservation, failure occurs in approximately 21.8% of patients ^[20]^C4. These failures are categorized by their spatial relationship to the original tumor and their temporal presentation relative to the completion of therapy.

Formal Definitions and Nomenclature

Also called: Treatment relapse, disease recurrence, oncologic failure, or organ function preservation failure (OFPF).

Locoregional Failure (LRF): The reappearance of disease at the primary tumor site (local) or in the regional lymph nodes (regional) ^[14]^B3b^[20]^C4. In sinonasal squamous cell carcinoma, local recurrence is the most common mode, occurring in 31.7% of patients ^[14]^B3b.
Distant Metastasis (DM): The development of disease in non-regional sites, such as the lungs, liver, or bone ^[4]^A1b^[14]^B3b.
Persistent Disease: The presence of viable tumor cells at the primary or regional site immediately following the completion of a planned CRT course, often identified during the first post-treatment evaluation ^[8]^B2b.
Organ Function Preservation Failure (OFPF): A composite endpoint defined as either local failure or pure functional failure (e.g., feeding tube dependence >2 years, permanent tracheostomy, or the need for major salvage surgery like total laryngectomy) in the absence of active tumor ^[20]^C4.

Classification of Recurrence Patterns

Failures are further classified by their relationship to the radiation treatment volumes to identify technical or biological resistance ^[14]^B3b.

Subtype	Definition	Incidence (SNSCC) ^[14]^B3b
In-field Failure	Recurrence occurring within the high-dose planning target volume (PTV)	55.7%
Marginal Failure	Recurrence at the edge of the radiation field or PTV	33.6%
Out-of-field Failure	Recurrence in areas not targeted by the high-dose radiation	10.7%

Clinical Significance

The development of failure significantly impacts survival and quality of life. For example, in T4 HPV-associated , 3-year locoregional recurrence rates reach 15% and distant metastasis rates reach 19% ^[18]^B3b. Identifying these patterns is essential for selecting salvage interventions, such as -based re-irradiation or minimally invasive options like photodynamic therapy (PDT) ^[8]^B2b^[9]^B2b.

Pearl: Organ function preservation failure (OFPF) occurs in over 20% of HNSCC patients, with T4 stage and active smoking serving as the strongest predictors of both oncologic and functional decline ^[20]^C4.

Spatial Classification of Local Recurrence

Pattern	Description	Clinical Implication
In-field	Within the 95% isodose volume	Suggests biological radioresistance
Marginal	At the PTV boundary	Suggests geographic miss or setup error
Out-of-field	Outside the treated volumes	Suggests occult disease at presentation

Spatial Patterns: In-field vs. Marginal vs. Out-of-field

▸In-field failure is the most frequent recurrence pattern in NPC, occurring in over 84% of cases, indicating biological resistance to standard dosing.
▸Marginal misses account for approximately 40% of failures in HPV-positive oropharyngeal cancer, highlighting the need for meticulous target volume delineation.
▸Sequential IMRT may reduce marginal failure rates compared to SIB-IMRT in postoperative oral cavity cancer by providing more homogeneous dose distributions.

HY High Yield: The addition of FDG-PET to CT-based planning can prevent geographic misses by identifying unsuspected regional nodal disease in 38% of patients and altering the longitudinal extent of the primary tumor in up to 81% of cases [21].

Locoregional failure following definitive chemoradiotherapy is characterized by its spatial relationship to the original planning target volumes (PTV). These failures are categorized based on the proportion of the recurrent tumor volume (Vrecur) that falls within the prescribed isodose lines or clinical target volumes (CTV). Accurate classification requires the rigid or deformable registration of diagnostic imaging at the time of recurrence back to the original planning computed tomography (CT) dataset ^[23]^D5^[25]^D5.

Definitions of Spatial Failure

Spatial failure is defined by the volumetric intersection of the recurrent tumor with the original treatment volumes ^[22]^B2b^[29]^D5:

In-field failure: >95% of the recurrent tumor volume falls within the CTV or the 95% isodose curve.
Marginal failure: 20% to 95% of the recurrent tumor volume is located within the CTV or 95% isodose curve.
Out-of-field failure: <20% of the recurrent tumor volume is located within the CTV or 95% isodose curve.

In-field Failure and Radioresistance

In-field failure remains the most common pattern of locoregional recurrence, particularly in nasopharyngeal carcinoma (NPC), where it accounts for 84.2% to 94.1% of recurrences ^[23]^D5. These failures typically occur within high-dose regions, suggesting biological radioresistance rather than technical delivery errors ^[23]^D5. In patients with receiving ( ) boosts, in-field control is high, but 76% of local recurrences that do occur are still classified as in-field by center of mass (COM) analysis ^[24]^D5.

Marginal Misses and Geographic Uncertainty

Marginal failures often represent a "geographic miss," where the tumor was present at the time of treatment but was not adequately covered by the high-dose volume. In -positive oropharyngeal cancer, marginal misses may account for 39% to 41% of recurrences ^[25]^D5. Technical factors influencing these rates include:

Target Delineation: Inadequate volume definition is a primary driver of marginal failure. The use of FDG-PET/CT can alter clinical staging in 38% of patients and identify PET-avid disease excluded by CT-only planning in 69% of cases ^[21]^B2b.
Treatment Technique: The use of simultaneous integrated boost (SIB) has been associated with higher marginal failure rates compared to sequential IMRT in some cohorts. In postoperative oral cavity cancer (OCC), marginal failure rates were 26.7% with SIB vs. 16.7% with sequential techniques ^[22]^B2b.
Anatomic Changes: Inter-fractional changes, such as weight loss or tumor shrinkage, can shift the target relative to the high-dose region. Adaptive replanning can mitigate this; in NPC, adaptive target volume reduction did not increase recurrences in the shrunken areas ^[23]^D5.

Out-of-field Failure and Elective Coverage

Out-of-field failures occur in regions not targeted by high-dose radiation, often in unirradiated neck levels or distant sites. While relatively rare in conventional NPC treatment (5.3% to 5.9%), they are more frequent in highly conformal techniques ^[23]^D5^[24]^D5. For example, SBRT boosts for oropharyngeal cancer showed a significantly higher out-of-field local failure rate of 24% compared to the 0%-5% reported for conventional regimens ^[24]^D5. Regional recurrences in these patients often occur in unirradiated neck levels (47%) or electively irradiated regions (42%) ^[24]^D5.

Comparative Failure Patterns by Site and Technique

Cancer Site	Technique	In-field Rate	Marginal Rate	Out-of-field Rate	Ref
NPC	Adaptive IMRT	94.1%	0%	5.9%	^[23]^D5
NPC	Standard IMRT	84.2%	10.5%	5.3%	^[23]^D5
Oral Cavity	SIB-IMRT	46.7%	26.7%	26.7%	^[22]^B2b
Oral Cavity	Sequential IMRT	50.0%	16.7%	33.3%	^[22]^B2b
Oropharynx (HPV+)	IMRT	40-45%	39-41%	17-18%	^[25]^D5

Pearl: In-field failure is the dominant pattern in NPC, whereas marginal misses are significantly more prevalent in HPV-positive oropharyngeal cancer, often due to inadequate target delineation that could be mitigated by PET-based planning ^[25]^D5^[27]^D5.

Spatial Failure Classification Criteria

Category	Volumetric Definition (Vrecur in CTV/95% Isodose)	Clinical Implication
In-field	>95%	Radioresistance
Marginal	20% to 95%	Geographic miss/Planning error
Out-of-field	<20%	Elective coverage failure

Temporal Patterns and Surveillance Timing

▸The highest risk for recurrence occurs within the first 14 to 24 months post-treatment, though late failures can emerge up to 5 years later.
▸PET/CT surveillance yield in clinically occult patients decreases from 9% at 12 months to 4% at 24 months.
▸Recovery duration of symptoms, such as cranial nerve palsy, serves as an independent prognostic factor for local relapse-free survival (HR 3.051).

HY High Yield: In patients with a negative 3-month post-treatment PET/CT, subsequent routine PET/CT surveillance at 12 and 24 months provides limited survival benefit compared to clinical detection of recurrence [41].

The temporal distribution of treatment failure following definitive chemoradiotherapy (CRT) is characterized by a high early incidence, with the majority of recurrences manifesting within the first 24 months. While specific data for mucosal squamous cell carcinoma (HNSCC) often emphasizes this two-year window, long-term surveillance remains critical due to the potential for late regional and distant failures ^[41]^B3b.

Peak Incidence and Early Recurrence

Recurrence risk is highest in the immediate post-treatment period. In related mucosal pathologies such as Barrett's esophagus, recurrence peaks at 14 months after achieving complete eradication and remains stable thereafter ^[30]^B2b. Similarly, in localized mucosa-associated lymphoid tissue (MALT) lymphoma of the head and neck, all patients typically achieve a complete response by a median of 3 months post-radiation, though relapses can occur at a median of 38.3 months ^[32]^C4. Early recurrence (within 3 months) in surgical contexts is often predicted by technical factors such as poor accessibility of lesion margins (OR 24.57, 95% CI 1.59-16.68) ^[39]^C4.

Surveillance Modalities and Timing

Surveillance protocols utilize serial imaging and clinical assessment to identify occult disease. The utility of (PET/CT) varies significantly by the timing of the scan:

3-Month PET/CT: Highly reliable for identifying persistent or recurrent disease ^[41]^B3b.
12-Month PET/CT: Detection rate of 9% in clinically occult patients ^[41]^B3b.
24-Month PET/CT: Detection rate drops to 4% in clinically occult patients ^[41]^B3b.

Notably, no significant difference in 3-year overall survival (60% vs 54%, P =.70) has been identified between recurrences detected via PET/CT surveillance versus those detected clinically in patients who had a negative 3-month scan ^[41]^B3b.

Late Failure and Long-term Risks

Late failures, occurring years after definitive therapy, necessitate extended follow-up, particularly for specific histological subtypes or complications. For instance, in thyroid-related malignancies, the median time to relapse can be approximately 5 years ^[37]^B3b, while reoperation for multinodular goiter occurs at a mean of 14.8 years ^[36]^B3b.

Beyond oncologic recurrence, clinicians must monitor for late-onset treatment complications that mimic or mask failure:

Carotid Stenosis: Patients with previous neck radiation may develop severe stenosis; carotid stenting is a durable option with a 10.8% long-term restenosis rate ^[43]^C4.
Dysphagia: Pharyngoesophageal junction (POJ) stenosis often requires intervention; the Kaplan-Meier estimate for dysphagia relapse after dilatation is 50% by 9.6 months ^[3]^A1b.
Vascular Events: Acute head and neck bleeding post-CRT may require transarterial embolization, with late recurrences presenting between 1 month and 5 years post-procedure ^[40]^C4.

Pearl: While the first 24 months represent the highest risk period for HNSCC recurrence, a negative 3-month PET/CT significantly diminishes the yield of subsequent routine PET surveillance, shifting the focus toward clinical assessment and management of late toxicities ^[41]^B3b.

PET/CT Surveillance Yield and Outcomes

Surveillance Interval	Detection Rate (Occult)	3-Year Overall Survival
3 Months	High Reliability	-
12 Months	9%	60% (PET-detected)
24 Months	4%	54% (Clinically detected)
P-value	-	0.70

Impact of HPV/p16 Status on Failure Patterns

▸HPV-positive OPC has significantly higher survival after progression (median 2.6 vs 0.8 years) despite similar median time to failure.
▸Locoregional failures in p16-positive disease are predominantly in-field (Type A), whereas p16-negative tumors are more prone to peripheral/marginal recurrences.
▸High nodal burden (≥5 nodes) in HPV-positive OPC shifts the failure pattern toward a high risk of distant metastasis, exceeding 50% at 3 years.

HY High Yield: Salvage surgery provides a 52% reduction in the risk of death after disease progression for both p16-positive and p16-negative patients (HR 0.48), emphasizing its role as the preferred salvage modality when feasible [49].

While the median time to disease progression is similar between p16-positive and p16-negative oropharyngeal squamous cell carcinoma (OPC) at approximately 7.3 to 8.2 months ^[49]^A1b, the spatial distribution and subsequent survival outcomes differ significantly. HPV-positive status is a robust independent predictor of overall survival (OS) after failure, with a 2-year OS after progression of 54.6% compared to 27.6% for p16-negative patients (HR 0.48, 95% CI 0.31-0.74) ^[49]^A1b.

Locoregional Failure Patterns

HPV-positive tumors demonstrate superior locoregional control (LRC) compared to HPV-negative disease, with 2-year LRC rates of versus 74% (p = 0.002) ^[56]^B3b. When locoregional recurrence (LRR) does occur, the geometric patterns of failure vary by p16 status:

In-field vs. Marginal: p16-positive tumors are more likely to fail centrally within the high-dose volume (Type A failure) ^[58]^D5. In contrast, p16-negative tumors are significantly more likely to exhibit peripheral or marginal recurrences (32% vs. 7%, p = 0.044) ^[58]^D5.
Extraneous Failures: p16-positive tumors exhibit a higher incidence of extraneous recurrences (Type E) outside the standard target volumes (17% vs. 0%) ^[58]^D5.
Nodal Burden: In p16-positive OPC, a high number of pathologically involved nodes (≥5) is a critical determinant of failure, increasing the 3-year LRR rate from 6% to 22% ^[51]^B3b.

Distant Metastasis and the 'Disseminated' Phenotype

Although HPV status does not significantly reduce the overall rate of distant metastasis (DM) compared to HPV-negative disease, it is associated with a unique "disseminated" or atypical failure phenotype ^[49]^A1b.

Feature	p16-Positive OPC	p16-Negative OPC
Predominant DM Site	Lung (72.9%) ^[49]^A1b	Lung (69.7%) ^[49]^A1b
Atypical Sites	Brain, skin, and multi-organ dissemination ^[49]^A1b	Primarily lung, liver, bone ^[49]^A1b
Nodal Influence	≥5 nodes increases 3-year DM to 53% ^[51]^B3b	Standard staging ^[49]^A1b
STING Expression	High STING predicts better DM control ^[60]^D5	Variable ^[60]^D5

Survival After Progression and Salvage

Survival after failure is markedly better in the HPV-positive population, even in the setting of distant disease. The median OS after progression is 2.6 years for p16-positive patients versus 0.8 years for p16-negative patients ^[49]^A1b.

Salvage Surgery: Curative-intent resection of LRR reduces the risk of death by 52% (HR 0.48, 95% CI 0.27-0.84) ^[49]^A1b.
Re-irradiation: HPV positivity remains a significant predictor of OS in the salvage setting using ( ), with a mean OS of 13.6 months compared to 6.88 months for HPV-negative recurrences ^[54]^B3b.
Solitary vs. Multi-site: Patients with a solitary recurrence (primary, neck, or oligometastatic) have a 5-year OS of 46%, whereas those with multi-site recurrence have a 5-year OS of only 9% ^[53]^B3b.

Controversies and Guideline Disagreement

Pearl: HPV status is the most powerful predictor of survival after failure; p16-positive patients survive nearly 2 years longer post-progression than p16-negative counterparts, justifying aggressive salvage even in recurrent disease ^[49]^A1b.

Distant Metastasis: Sites and Risk Factors

▸The lungs, liver, and bone are the most frequent sites of visceral distant metastasis, while non-regional nodes (supraclavicular, para-aortic) represent common lymphatic systemic failure.
▸Pathological N2-N3 status and imaging-detected extranodal extension (iENE) are the strongest independent predictors of distant progression and poor overall survival.
▸Oligometastatic disease (≤5 lesions) may benefit from consolidative radiotherapy to both primary and metastatic sites, extending median PFS compared to systemic therapy alone.

HY High Yield: In patients with T4 disease and extensive nodal involvement (pN2-3), the risk of distant metastasis as the initial site of failure exceeds 75% within 2 years, often rendering aggressive combined organ resection futile [73].

While definitive chemoradiotherapy (CRT) aims for locoregional control, distant metastasis (DM) remains a primary driver of mortality in advanced head and neck and esophageal squamous cell carcinomas. The transition from locoregional disease to systemic failure often follows a predictable spatial distribution, with specific clinical and pathological markers identifying patients at high risk for out-of-field progression.

Common Sites of Distant Failure

The distribution of distant failure is influenced by the primary tumor's lymphatic drainage and biological aggressiveness. In esophageal squamous cell carcinoma (ESCC), the 5-year cumulative incidence of distant recurrence following neoadjuvant CRT and surgery is 24.3% ^[66]^B2b.

Lungs: Frequently the most common site of visceral metastasis in squamous cell carcinomas of the upper aerodigestive tract ^[78]^B3b.
Liver and Bone: Common secondary sites for hematogenous spread ^[78]^B3b.
Non-regional Lymph Nodes: In ESCC, non-regional nodal involvement (Stage IVB) often involves the supraclavicular, para-aortic, and retroperitoneal stations ^[81]^B3b.
Rare Sites: Metastases may also occur in the brain, adrenal glands, soft tissue, and pleura ^[78]^B3b.

Clinical and Pathological Risk Factors

Independent predictors of distant failure are primarily related to the extent of the initial nodal burden and the presence of aggressive features at the primary site. In patients with T4 disease, the decision for aggressive local intervention must be weighed against the high risk of early postoperative distant progression, which occurs as the initial site of failure in 54.8% of cases ^[73]^B3b.

Factor	OR/RR/HR (with 95% CI)	Plain-English meaning	Independent?	Reference
pN2-3 Nodal Status	HR 2.14 (1.45-3.17)	Over twice the risk of distant progression compared to lower nodal stages.	Yes	^[73]^B3b
pM1 (Initial)	HR 2.11 (1.22-3.64)	Initial distant involvement strongly predicts subsequent systemic failure.	Yes	^[73]^B3b
iENE (Imaging ENE)	AHR 2.43 (1.96-3.03)	Radiographic extranodal extension more than doubles the risk of death/failure.	Yes	^[67]^B2b
Lymphovascular Invasion	Not reported	Presence of tumor in vessels; associated with higher recurrence risk.	Yes	^[75]^B3b^[80]^B3b
Perineural Invasion	HR 4.496 (p=0.019)	Nearly 4.5 times the odds of recurrence or metastasis.	Yes	^[80]^B3b

Nodal Burden and Staging Implications

Nodal characteristics are the strongest prognosticators for systemic escape. In salivary gland carcinomas, the number of positive nodes significantly impacts survival; the risk of death increases from an adjusted hazard ratio (aHR) of 1.70 for one node to 2.46 for four nodes ^[74]^B3b. Similarly, in HPV-associated oropharyngeal carcinoma, imaging-detected extranodal extension (iENE) is the most potent nodal feature, with iENE-positive disease carrying a hazard ratio of 2.43 (95% CI 1.96-3.03) for overall survival ^[67]^B2b.

In esophageal contexts, cervical lymph node metastasis (CLNM) occupies a conceptual border between locoregional and distant disease ^[64]^B2b. While historically viewed as M1a, contemporary staging often treats these as regional (N) disease due to the longitudinal lymphatic drainage of the esophagus ^[64]^B2b. Patients with higher cN stages and poorer performance status consistently show increased mortality risks ^[64]^B2b.

Oligometastatic Disease (OMD)

Oligometastatic failure, defined as up to five measurable lesions across up to three organs, represents an intermediate state where local therapy may still provide a survival benefit ^[78]^B3b. In these patients, adding radiotherapy to systemic immunochemotherapy improved median progression-free survival from 7.7 months to 13.0 months (HR 0.52, 95% CI 0.388-0.696); NNT not calculable from reported data ^[78]^B3b. This benefit is most pronounced when radiotherapy targets both the primary tumor and all metastatic sites ^[78]^B3b^[81]^B3b.

Pearl: In T4 disease or cases with pN2-3 nodal involvement, the 2-year distant progression rate can reach 76.3% to 78.3%, necessitating a high index of suspicion for systemic failure during surveillance ^[73]^B3b.

Predictors of Distant Progression in Advanced Squamous Cell Carcinoma

Risk Factor	Hazard Ratio (95% CI)	Clinical Significance
pN2-3 Nodal Stage	2.14 (1.45-3.17)	Primary predictor of distant failure in T4 disease ^[73]^B3b
Imaging ENE (iENE)	2.43 (1.96-3.03)	Strongest prognostic nodal feature in HPV+ OPC ^[67]^B2b
pM1 at Diagnosis	2.11 (1.22-3.64)	High risk for subsequent multi-organ failure ^[73]^B3b
Perineural Invasion	4.496 (p=0.019)	Independent factor for recurrence and metastasis ^[80]^B3b

Biological and Molecular Drivers of Resistance

▸Hypoxia (TMR ≥1.6) is a dominant driver of locoregional failure, especially in HPV-negative HNSCC where recurrence risk reaches 57% [82].
▸Hypoxia-induced exosomal miR-455 promotes metastasis in nasopharyngeal carcinoma by targeting ZO-1 to increase vascular permeability [86].
▸CD11b+ cell recruitment to hypoxic areas following treatment triggers lymphangiogenesis and cervical lymph node relapse [85].

HY High Yield: In patients receiving ARCON, high CA-IX expression (>25%) paradoxically correlates with improved locoregional control (P=0.04), suggesting that oxygenation-modifying therapies can overcome traditional hypoxic resistance markers [83].

While distant failure patterns are increasingly recognized, the biological milieu of the primary tumor remains the principal driver of chemoradiotherapy resistance. Hypoxia and proliferation-specific parameters are the primary factors responsible for treatment failure, alongside the emerging role of cancer stem cells ^[84]^D5. These biological drivers create a microenvironment that actively resists ionizing radiation and promotes metastatic spread through molecular signaling pathways.

Hypoxia-Mediated Radioresistance

Tumor hypoxia significantly impairs the efficacy of primary radiotherapy (RT). In a prospective cohort, patients with more hypoxic tumors (defined by a tumor-to-muscle ratio [TMR] ≥1.6 on 18F-FAZA PET/CT) demonstrated a significantly higher risk of locoregional recurrence compared to those with less hypoxic tumors (44% vs 9%, HR 5.8 [1.2-28.2]) ^[82]^C4. This resistance is particularly pronounced in specific molecular subtypes:

HPV-Negative Status: The risk of locoregional recurrence is highest in patients with more hypoxic, non-OPCp16+ tumors, reaching 57% [21-94%] ^[82]^C4.
Spatial Correlation: Recurrences often overlap with baseline hypoxic subvolumes, though co-registration shows that failures can also occur in adjacent regions ^[82]^C4.
Endogenous Markers: Markers such as CA-IX, Glut-1, and Glut-3 are used to identify hypoxic regions. High Glut-1 intensity is associated with a worse overall survival (P = 0.001) and an increased rate of distant metastases (P = 0.0005) ^[83]^B2b.

Molecular Pathways of Metastasis and Relapse

Hypoxia does not merely cause passive resistance; it actively stimulates pathways that facilitate tumor progression and lymph node (LN) metastasis. In (NPC), hypoxia induces the release of exosomes containing miR-455 in a HIF-1α-dependent manner ^[86]^D5. This exosomal miR-455 targets zonula occludens 1 (ZO-1), which increases vascular permeability and promotes transendothelial invasion ^[86]^D5.

In oral cancers, hypoxia is strongly associated with the influx of CD11b+ cells ^[85]^D5. These cells are recruited into hypoxic areas following treatment, where they stimulate lymphangiogenesis and re-vascularization, leading to cervical LN metastasis and relapse ^[85]^D5.

Prognostic Markers and Treatment Modification

The relationship between molecular markers and outcome can be altered by oxygenation-modifying treatments like ARCON (accelerated radiotherapy with carbogen and nicotinamide). Under ARCON, the typical negative prognostic impact of CA-IX and Glut-3 may be reversed; for instance, high CA-IX positivity (>25% of tumor area) was associated with better locoregional control (P = 0.04) and freedom from distant metastases (P = 0.02) in this context ^[83]^B2b.

Marker	Biological Role	Clinical Impact (Standard RT)
18F-FAZA PET (TMR ≥1.6)	Imaging of hypoxic volume	HR 5.8 for locoregional failure ^[82]^C4
Glut-1	Glucose transporter	Increased distant metastasis and worse OS ^[83]^B2b
miR-455	Exosomal microRNA	Increased vascular permeability via ZO-1 targeting ^[86]^D5
CD11b+ Cells	Immune cell influx	Promotion of lymphangiogenesis and LN metastasis ^[85]^D5

These molecular drivers of resistance necessitate precise technical execution of radiotherapy to ensure that high-risk biological subvolumes are adequately covered, a topic addressed in the following section on technical factors influencing failure.

Pearl: A baseline FAZA PET TMR ≥1.6 identifies a high-risk phenotype with a nearly six-fold increase in locoregional failure risk (HR 5.8), particularly in HPV-negative disease ^[82]^C4.

Molecular Drivers of Resistance and Metastasis

Factor	Mechanism	Clinical Outcome
Hypoxia (FAZA PET)	Radioresistance	44% recurrence rate in high-uptake tumors ^[82]^C4
HIF-1α/miR-455	Vascular permeability	Increased transendothelial invasion and metastasis ^[86]^D5
CD11b+ Influx	Lymphangiogenesis	Uncontrolled cervical lymph node metastasis ^[85]^D5
Glut-1 Intensity	Metabolic adaptation	Worse overall survival (P=0.001) ^[83]^B2b

Technical Factors Influencing Failure

▸Treatment interruptions exceeding 5 days are significantly more frequent with 2DRT (69%) than IMRT (42.5%), directly correlating with worse overall survival.
▸A minimum point dose (Dmin) ≥54.0 Gy to the primary gross tumor volume is a primary technical predictor of local failure-free survival in T3-4 nasopharyngeal carcinoma.
▸Mandibular V44 <42% and V58 <25% are identified thresholds to minimize the risk of osteoradionecrosis in oropharyngeal cancer patients.

HY High Yield: In T4 NPC with residual primary lesions after radical IMRT, an IMRT boost of 4 to 6.75 Gy significantly improves 3-year overall survival (86.6% vs 72.7%) and local recurrence-free survival (93.4% vs 83.5%) [94].

Beyond the biological drivers of resistance, the precision of delivery and the management of treatment interruptions are critical determinants of locoregional control. Technical execution, specifically regarding target volume definition and dose-volume constraints, directly impacts both the risk of recurrence and the severity of treatment-limiting toxicities that can necessitate therapy breaks ^[92]^B2b.

Target Volume Definition and Dose Thresholds

In nasopharyngeal carcinoma (NPC), reducing the intensity-modulated radiotherapy ( ) target volume after induction chemotherapy (IC) has been shown to improve quality of life without compromising local control ^[87]^A1b. A prospective trial demonstrated that planning IMRT based on post-IC images resulted in 3-year locoregional failure-free survival (LRFFS) of 93.9% compared to 91.8% when using pre-IC images ^[87]^A1b. For advanced T3-4 NPC, the minimum point dose (Dmin) to the primary gross tumor volume (GTV_P) is a significant prognostic factor; a Dmin ≥54.0 Gy is associated with superior 3-year LFFS (95.9% vs 78.4%, P = 0.005) and overall survival ^[101]^B2b. In cases of residual primary lesions after radical IMRT, an additional boost dose of 4 to 6.75 Gy in 2-3 fractions significantly improves 3-year local recurrence-free survival from 83.5% to 93.4% ^[94]^B3b.

Treatment Interruptions and Modality Impact

Treatment continuity is a primary driver of survival outcomes. Real-world data indicate that conventional 2D radiotherapy (2DRT) is associated with higher rates of treatment interruptions exceeding 5 days compared to modern techniques (69% for 2DRT vs 42.5% for IMRT) ^[92]^B2b. These interruptions contribute to significantly worse overall survival in patients receiving 2DRT ^[92]^B2b. While IMRT and ( ) offer similar biophysical skin response profiles, the superficial skin dose independently predicts long-term barrier dysfunction, such as reduced hydration and sebum levels at 3 months post-RT ^[89]^B2b.

Dosimetric Predictors of Toxicity-Related Failure

Severe toxicities often lead to treatment de-escalation or cessation, indirectly influencing failure rates. Key dosimetric thresholds for organs at risk (OAR) include:

Salivary Glands: A mean dose (Dmean) to the parotid glands of 24 Gy represents the 50% tolerance dose for developing acute grade ≥2 taste dysfunction ^[102]^B3b. The combined dose to contralateral parotid and submandibular glands correlates most strongly with patient-reported ^[93]^B2b.
Masticatory Muscles: To prevent trismus in advanced NPC, proposed constraints include a digastric muscle Dmean ≤26 Gy and mylohyoid Dmean ≤28 Gy ^[105]^B3b.
Mandible: Osteoradionecrosis (ORN) risk increases significantly when the mandible volume receiving 44 Gy (V44) is ≥42% and the V58 is ≥25% ^[99]^C4.
Thyroid: Hypothyroidism risk is significantly higher when the thyroid volume receiving 45 Gy (V45) exceeds 67%, particularly in patients who have undergone neck dissection ^[106]^C4.

Regional Control and Elective Volumes

Elective nodal irradiation remains a technical balance between regional control and late toxicity. In , a dose-dependent risk reduction for regional recurrence is observed in the elective treatment interval of 40 to 50 Gy (OR = 0.18, p < 0.05) ^[91]^B2b. Interestingly, while recurrences within the elective or tumor target volumes are associated with poor survival, regional recurrences occurring outside the planned target volumes do not appear to significantly decrease overall survival, suggesting that limited elective volumes may be feasible in select cases ^[91]^B2b. These technical considerations regarding volume and dose directly inform the discussed in the following section.

Pearl: Maintaining a minimum point dose (Dmin) of at least 54 Gy to the primary tumor volume in advanced NPC is critical for local control, as doses below this threshold are associated with a nearly four-fold increase in the risk of 3-year local failure ^[101]^B2b.

Dosimetric Thresholds for Toxicity Prevention

Organ at Risk	Parameter	Threshold	Clinical Impact
Parotid Glands	Dmean	24 Gy	50% risk of Grade ≥2 acute taste dysfunction ^[102]^B3b
Mandible	V44 / V58	<42% / <25%	Reduced risk of osteoradionecrosis ^[99]^C4
Thyroid	V45	≤67%	Reduced risk of radiation-induced hypothyroidism ^[106]^C4
Digastric Muscle	Dmean	≤26 Gy	Prevention of trismus in advanced NPC ^[105]^B3b
Mylohyoid Muscle	Dmean	≤28 Gy	Prevention of trismus in advanced NPC ^[105]^B3b

Salvage Options and Outcomes After Failure

▸Salvage surgery remains the gold standard for resectable HNSCC recurrence, with 5-year OS rates ranging from 15.5% in the hypopharynx to over 40% in the oral cavity.
▸The integration of hyperthermia with salvage chemoradiotherapy for unresectable disease can achieve an ORR of 82.9% and a median OS of 32.8 months, significantly exceeding historical benchmarks.
▸Minimally invasive techniques like TORS and endoscopic nasopharyngectomy offer comparable oncologic outcomes to open surgery with significantly reduced functional morbidity and shorter hospital stays.

HY High Yield: In recurrent oral cavity cancer, the interval to recurrence is a major prognostic driver: 5-year OS is 63.8% for late relapse versus only 30.0% for early relapse (p = 0.004) [114].

! Warning: Salvage surgery in previously irradiated fields carries a high risk of major complications, including carotid artery rupture (up to 13.3% in hypopharyngeal cases) and chronic feeding tube dependence (up to 41% in open oral/oropharyngeal resections) [115, 117].

Salvage management for recurrent head and neck squamous cell carcinoma (HNSCC) following definitive chemoradiotherapy (CRT) requires intensive multidisciplinary coordination to balance curative intent with functional preservation ^[107]^A1c. While salvage surgery remains the primary curative option for resectable disease, outcomes vary significantly by subsite and tumor burden ^[112]^B2a^[120]^B3b. For unresectable recurrences, emerging strategies include chemoimmunotherapy and the integration of hyperthermia with re-irradiation ^[109]^B2b^[110]^B2b.

Salvage Surgery and Functional Outcomes

Surgical salvage is the only curative intent option for many patients, though it carries a high risk of continued functional impairment ^[112]^B2a^[120]^B3b. Surgical margins serve as the most consistent prognosticator for disease-free survival (HR 0.49, p < 0.001) and local control (HR 0.49, p < 0.001) ^[120]^B3b.

Oral Cavity: Salvage surgery for recurrent oral cavity cancer (rOCC) yields a 5-year overall survival (OS) of 43.0% ^[114]^B2a. Outcomes are superior in patients with late relapse (63.8% vs. 30.0% for early relapse, p = 0.004) ^[114]^B2a.
Oropharynx: (TORS) is increasingly utilized for early T- and N-classification recurrences, demonstrating a 2-year OS of 68.5% compared to 45.9% for open surgery (p = 0.03) ^[111]^B2a. TORS is associated with lower rates of long-term tracheostomy (0%-11.5%) and feeding tube dependence ^[111]^B2a^[112]^B2a.
Larynx and Hypopharynx: Supracricoid partial laryngectomy (SCPL) as a salvage procedure achieves a 5-year disease-specific survival (DSS) of 100% in qualifying patients, with a 10.3% local recurrence rate ^[116]^B2a. Conversely, hypopharyngeal salvage has a guarded prognosis, with 5-year OS ranging from 15.5% to 57.1% and high complication rates, including pharyngocutaneous fistula (up to 71.4%) ^[115]^B2a.
Nasopharynx: Endoscopic nasopharyngectomy for recurrent nasopharyngeal carcinoma (rNPC) provides significantly improved 5-year OS compared to re-irradiation with (p = 0.016) ^[118]^B2a.

Non-Surgical Salvage and Re-irradiation

For patients unfit for surgery, re-irradiation combined with sensitizing agents is employed. The addition of hyperthermia to salvage concurrent CRT (50 Gy in 22 fractions) for unresectable disease has demonstrated an overall response rate (ORR) of 82.9% and a median OS of 32.8 months ^[110]^B2b. This approach significantly outperforms historical non-surgical outcomes, where response rates for immunotherapy alone are often less than 20% ^[110]^B2b.

Emerging Systemic and Immunotherapy Strategies

Novel protocols are integrating immune checkpoint inhibitors into the salvage timeline. A phase II trial of preoperative (200 mg) plus chemotherapy followed by surgery and adjuvant tislelizumab reported a 2-year OS of 54.8% ^[109]^B2b. In this setting, R0 resection was achieved in 73.1% of surgical patients, with a pathologic complete response (pCR) rate of 15.4% ^[109]^B2b. For high-risk patients whose 5-year DSS is predicted to be below 20% with surgery, immunotherapy may offer a reasonable alternative with reduced morbidity ^[122]^B3b.

Prognostic Factors for Salvage

Factor	Favorable Prognosis	Poor Prognosis
Relapse Timing	Late relapse (>2 years) ^[114]^B2a	Early relapse ^[114]^B2a
Surgical Margins	R0 (Negative) ^[109]^B2b^[120]^B3b	Positive margins ^[112]^B2a^[120]^B3b
Nodal Status	rcN0 or rcN1 ^[122]^B3b	Advanced nodal disease (rN2-3) ^[123]^B3b
Subsite	Larynx (SCPL eligible) ^[116]^B2a	Hypopharynx ^[115]^B2a^[122]^B3b
Biomarkers	Low BCR clonality ^[109]^B2b	High baseline BCR clonality ^[109]^B2b

Pearl: Surgical margins are the most critical modifiable prognostic factor in salvage surgery; achieving an R0 resection reduces the risk of local failure by approximately 51% (HR 0.49) ^[120]^B3b.

Comparison of Salvage Modalities and Outcomes

Modality	Patient Population	Primary Outcome	Complications/Morbidity
Salvage TORS	Early rOPSCC ^[111]^B2a	2-year OS: 68.5%	32.3% pooled complication rate ^[112]^B2a
Salvage SCPL	Select rLarynx ^[116]^B2a	5-year DSS: 100%	4.76% G-tube dependency ^[116]^B2a
CCRT + Hyperthermia	Unresectable rHNSCC ^[110]^B2b	Median OS: 32.8 mo	12 cases of osteonecrosis ^[110]^B2b
Chemoimmunotherapy + Surgery	Resectable rHNSCC ^[109]^B2b	2-year OS: 54.8%	Grade 3 hyperglycemia (rare) ^[109]^B2b
Endoscopic Nasopharyngectomy	rT3-T4 NPC ^[113]^B2a	2-year OS: 34.6-88.7%	Minor/transient; rare hemorrhage ^[113]^B2a

Landmark Trials Reporting Failure Patterns

▸Adding cetuximab to cisplatin-RT does not reduce locoregional or distant failure rates in locally advanced HNSCC, regardless of p16 status.
▸Nivolumab added to postoperative cisplatin-RT significantly improves disease-free survival in high-risk resected HNSCC (HR 0.76).
▸Accelerated radiotherapy improves locoregional control in glottic SCC (HR 0.72) but does not consistently improve survival in broader HNSCC cohorts when compared to standard chemoradiotherapy.

HY High Yield: In the DAHANCA 10 trial, attempting to correct low hemoglobin (<14.0 g/dl) with darbepoetin alfa during radiotherapy actually increased the 5-year locoregional failure rate from 34% to 47% (HR 1.53) and worsened overall survival (HR 1.30).

The evolution of definitive chemoradiotherapy (CRT) has been shaped by trials investigating treatment intensification, fractionation schedules, and the addition of targeted agents. While these interventions often aim to reduce locoregional failure (LRF), they frequently highlight the persistent challenge of distant metastasis and the prognostic significance of p16 status in failure distribution.

Impact of Treatment Intensification and Fractionation

Landmark trials have demonstrated that while accelerated radiotherapy (RT) can improve local control, it may not translate to a survival benefit when compared to standard CRT. The GORTEC 99-02 trial found that conventional CRT (70 Gy in 7 weeks with -fluorouracil) improved progression-free survival (PFS) compared to very accelerated RT alone (64.8 Gy in 3.5 weeks; HR 0.82, 95% CI 0.67-0.99, p=0.041), but adding acceleration to chemotherapy (70 Gy in 6 weeks) offered no additional PFS benefit (HR 1.02, 95% CI 0.84-1.23) ^[128]^A1b. In specific anatomical sites, such as glottic squamous cell carcinoma, the DAHANCA 6 trial showed that moderate acceleration (6 vs 5 weekly fractions) significantly reduced the cumulative incidence of LRF from 29.3% to 21.6% (HR 0.72, 95% CI 0.53-0.97, p=0.04) ^[140]^A1b.

For advanced N3 disease, outcomes remain poor regardless of intensification. A pooled analysis of GORTEC trials showed a 5-year overall survival (OS) of only 13.8%, with no significant difference between CRT and very accelerated RT in terms of LRF (HR 0.70, p=0.13) or distant progression (HR 0.86, p=0.53) ^[138]^A1b.

Targeted Therapy and Immunotherapy Integration

Attempts to reduce failure rates by adding EGFR inhibitors to standard regimens have largely been unsuccessful in phase III settings. The RTOG 0522 trial, with over 10 years of follow-up, confirmed that adding to radiation and did not reduce LRF (HR 1.21, p=0.94) or distant metastasis (HR 0.79, p=0.10) ^[130]^A1b. Similarly, the DAHANCA 19 trial found that the EGFR inhibitor did not improve the 5-year LRF rate (24% vs 18% in control; HR 1.16, 95% CI 0.84-1.59) ^[135]^A1b.

In the postoperative high-risk setting, the GORTEC 2018-01 NIVOPOST-OP trial recently demonstrated that adding (240 mg followed by 360 mg concomitantly and 480 mg adjuvantly) to and RT significantly improved disease-free survival (DFS) compared to CRT alone (HR 0.76, 95% CI 0.60-0.98, p=0.034) ^[127]^A1b. Conversely, maintenance therapy with following postoperative CRT failed to improve 2-year DFS (61% vs 64% for placebo; HR 1.12) ^[136]^A1b.

Risk Stratification and Institutional Factors

Failure patterns are heavily influenced by p16 status and institutional experience. RTOG 0129 established risk groups based on p16 status, smoking history, and T-stage, which were validated in RTOG 0522 ^[132]^A1b.

Low-risk (p16-positive): 5-year OS of 88.1% and PFS of 72.9% ^[132]^A1b.
High-risk (p16-negative): 5-year OS of 45.1% and PFS of 42.2% ^[132]^A1b.

Institutional volume also serves as a critical determinant of failure. Patients treated at low-accruing centers (median 4 patients) had a 91% increased risk of death (HR 1.91, 95% CI 1.37-2.65) compared to high-accruing centers (median 65 patients), even after adjusting for RT protocol deviations ^[139]^A1b.

Failure Patterns in Larynx Preservation

In the GORTEC 2000-01 trial, induction chemotherapy with TPF ( , , and ) significantly improved 10-year larynx preservation rates compared to PF (70.3% vs 46.5%) ^[129]^A1b. This regimen also improved larynx dysfunction-free survival (63.7% vs 37.2% at 10 years, p=0.001) ^[129]^A1b.

Pearl: Institutional experience is a major independent prognostic factor; treatment at low-volume centers is associated with a 72% to 91% increase in mortality risk regardless of radiotherapy compliance ^[139]^A1b.

Failure and Survival Outcomes by RTOG Risk Group (RTOG 0522 Validation)

Risk Group	5-Year OS	5-Year PFS	Key Characteristics
Low Risk	88.1%	72.9%	p16+, ≤10 pack-years smoking
Intermediate Risk	69.9%	56.1%	p16+, >10 pack-years OR p16-, ≤10 pack-years, T2-3
High Risk	45.1%	42.2%	p16-, >10 pack-years OR T4 disease

Future Directions: Adaptive Radiotherapy and Radiomics

▸Delta-radiomics, which measures imaging feature changes during treatment, consistently outperforms static baseline radiomics for predicting both tumor response and late toxicities.
▸Habitat-based modeling, which segments tumors into subregions with distinct biological properties (e.g., high-entropy or specific T1/T2 values), provides superior predictive accuracy for nodal metastasis compared to whole-tumor analysis.
▸External validation remains the primary barrier to clinical implementation, as many high-performing internal models fail to maintain accuracy when applied to independent multicenter datasets.

HY High Yield: SHAP (Shapley Additive Explanations) analysis is increasingly used to improve AI interpretability by identifying which specific radiomic features (e.g., intensity kurtosis or comorbidities) drive a model's prediction of failure [162, 164].

! Warning: Clinicians should exercise caution with radiomic tools lacking external validation; one study of six published parotid models found AUCs dropped from >0.90 in original reports to <0.64 upon independent testing [165].

Technological advancements in adaptive radiotherapy and radiomics aim to address the biological heterogeneity that drives treatment failure in HNSCC. By integrating longitudinal imaging with machine learning, clinicians can potentially identify early indicators of resistance and modify treatment volumes or doses in real-time. These approaches move beyond static baseline assessments to capture the dynamic evolution of tumor and normal tissue during the 6 to 7 weeks of definitive chemoradiotherapy ^[162]^B3b.

Radiomics and AI for Failure Prediction

Radiomics enables the extraction of high-dimensional features from standard imaging that are imperceptible to the human eye. In oral tongue squamous cell carcinoma (OTSCC), MRI-based radiomics and deep learning have shown preliminary promise in predicting recurrence and prognostic outcomes, though evidence is currently limited by retrospective designs and low certainty ^[147]^B2a.

Malignancy Discrimination: CT-based deep learning models have achieved an externally validated AUC of 0.890 (95% CI: 0.844-0.937) for differentiating benign from malignant parotid masses ^[148]^C4.
Nodal Metastasis: Radiopathomics models, which combine ultrasound features with cytology-derived pathomics, have improved the prediction of extrathyroidal extension in papillary thyroid carcinoma, reaching an AUC of 0.873 in external validation ^[159]^B3b.
Habitat Imaging: Clustering intratumoral subregions into "habitats" based on entropy or quantitative T1/T2 maps has outperformed whole-tumor models in predicting lymph node metastasis in esophageal and oral cancers ^[160]^B3b^[164]^B3b.

Delta-Radiomics and Adaptive Monitoring

Delta-radiomics, the analysis of feature changes over the course of treatment, frequently outperforms static baseline models ^[154]^B2a. This is particularly relevant for predicting treatment-induced toxicities like , where parotid gland changes on weekly -CBCT can be captured ^[162]^B3b.

Xerostomia Prediction: SVM models using delta-radiomics from week-4 of treatment achieved an AUC of 0.79 for predicting late radiation-induced xerostomia ^[162]^B3b.
Response Assessment: MRI-based DeltaHabitat models have demonstrated an AUC of 0.878 (95% CI: 0.791-0.964) in predicting pathological complete response (pCR) in patients receiving neoadjuvant chemoimmunotherapy ^[156]^C4.

Molecular and PET/CT Integration

Future strategies involve "multiomics" frameworks that link functional imaging with underlying genomic programs. In HPV-negative HNSCC, activation of the Hedgehog (HH) signaling pathway has been correlated with specific [18F]FDG PET/CT radiomic features, such as peak uptake (histogram:ih.max), which is associated with inferior survival ^[166]^B3b. Pharmacologic inhibition of these pathways has been shown to induce measurable reductions in [18F]FDG uptake in preclinical models, suggesting that PET-based radiomics could serve as a non-invasive surrogate for monitoring therapeutic response to targeted agents ^[166]^B3b.

Controversies and Guideline Disagreement

Question	Position A	Position B	Strength	Implication
Clinical Reproducibility	Radiomic models show high internal AUC (>0.90) ^[165]^B3b.	External validation often fails to replicate results (AUCs 0.52-0.63) ^[165]^B3b.	Moderate	Current models lack generalizability for routine use.
Model Complexity	Multimodal fusion (CT + biomarkers) improves AUC to 0.93 ^[150]^B2b.	Radiomics-only models show modest gains over clinical variables ^[153]^B2a.	Low	Incremental value of AI over standard care is still being quantified.

Pearl: Delta-radiomics features from week-4 of radiotherapy are more predictive of long-term failure and toxicity than baseline static imaging, providing a critical window for adaptive treatment modification ^[162]^B3b.

Performance of AI Models in Failure and Risk Prediction

Application	Modality	Best Metric (AUC)	Validation Type
Parotid Malignancy	CT (Deep Learning)	0.890 ^[148]^C4	External
Nodal Metastasis (ESCC)	CT (Habitat)	0.844 ^[160]^B3b	External
pCR Prediction (OCSCC)	MRI (DeltaHabitat)	0.878 ^[156]^C4	Internal
Xerostomia (HNC)	CBCT (Delta-Radiomics)	0.790 ^[162]^B3b	Internal
Nodal Staging (PTC)	Ultrasound (Radiomics)	0.830 ^[153]^B2a	Meta-analysis

References

[1]
Xu C, Liang XY, Huang XQ et al.. “Toripalimab Combination Therapy Without Concurrent Cisplatin for Nasopharyngeal Carcinoma: The DIAMOND Randomized Clinical Trial.” JAMA (2025). PMID: 40839372 ↗
L1RCTCited in: Introduction and Definitions of Failure
[2]
Zhu H, Rivin Del Campo E, Ye J et al.. “Involved-Field Irradiation in Definitive Chemoradiotherapy for Locoregional Esophageal Squamous Cell Carcinoma: Results From the ESO-Shanghai 1 Trial.” International journal of radiation oncology, biology, physics (2021). PMID: 33677048 ↗
L1RCTCited in: Introduction and Definitions of Failure
[3]
Wu PI, Szczesniak MM, Maclean J et al.. “Endoscopic dilatation improves long-term dysphagia following head and neck cancer therapies: a randomized control trial.” Diseases of the esophagus : official journal of the International Society for Diseases of the Esophagus (2019). PMID: 30462194 ↗
L1RCTCited in: Introduction and Definitions of Failure, Temporal Patterns and Surveillance Timing
[4]
Yi J, Huang X, Xu Z et al.. “Phase III randomized trial of preoperative concurrent chemoradiotherapy versus preoperative radiotherapy for patients with locally advanced head and neck squamous cell carcinoma.” Oncotarget (2017). PMID: 28179586 ↗
L1RCTCited in: Introduction and Definitions of Failure
[5]
Li Y, Liu H, Sun C et al.. “Comparison of Clinical Efficacy of Neoadjuvant Chemoradiation Therapy Between Lower and Higher Radiation Doses for Carcinoma of the Esophagus and Gastroesophageal Junction: A Systematic Review.” International journal of radiation oncology, biology, physics (2021). PMID: 33964352 ↗
L2SR_COHORTCited in: Introduction and Definitions of Failure
[6]
Chung SR, Choi YJ, Suh CH et al.. “Diffusion-weighted Magnetic Resonance Imaging for Predicting Response to Chemoradiation Therapy for Head and Neck Squamous Cell Carcinoma: A Systematic Review.” Korean journal of radiology (2019). PMID: 30887747 ↗
L2SR_COHORTCited in: Introduction and Definitions of Failure
[7]
Lin Y, Dong H, Deng W et al.. “Evaluation of Salivary Exosomal Chimeric GOLM1-NAA35 RNA as a Potential Biomarker in Esophageal Carcinoma.” Clinical cancer research : an official journal of the American Association for Cancer Research (2019). PMID: 30745298 ↗
L2PROSPECTIVE_COHORTCited in: Introduction and Definitions of Failure
[8]
Horimatsu T, Yano T, Yamamoto Y et al.. “Long-term outcome of PDT for local failure after CRT or RT for oesophageal cancer.” Journal of gastroenterology (2025). PMID: 41219541 ↗
L2NON_RANDOMIZED_TRIALCited in: Introduction and Definitions of Failure
[9]
Awan MJ, Nedzi L, Wang D et al.. “Final results of a multi-institutional phase II trial of reirradiation with concurrent weekly cisplatin and cetuximab for recurrent or second primary squamous cell carcinoma of the head and neck.” Annals of oncology : official journal of the European Society for Medical Oncology (2018). PMID: 29346519 ↗
L2NON_RANDOMIZED_TRIALCited in: Introduction and Definitions of Failure
[10]
Song T, Zhang X, Fang M et al.. “Long-term results of definitive concurrent chemoradiotherapy using paclitaxel plus oxaliplatin in unresectable locally advanced esophageal cancer: a prospective phase II trial.” Cancer medicine (2016). PMID: 27925455 ↗
L2NON_RANDOMIZED_TRIALCited in: Introduction and Definitions of Failure
[11]
Gou XX, Jin F, Wu WL et al.. “Induction chronomodulated chemotherapy plus radiotherapy for nasopharyngeal carcinoma: A Phase II prospective randomized study.” Journal of cancer research and therapeutics (2018). PMID: 30589048 ↗
L2RCT_PHASE2Cited in: Introduction and Definitions of Failure
[12]
Hattori A, Kadota T, Yamashita H et al.. “Efficacy and safety of photodynamic therapy using an ultra-thin endoscope for local failure with esophageal stenosis after chemoradiotherapy for esophageal cancer.” Esophagus : official journal of the Japan Esophageal Society (2026). PMID: 42230512 ↗
L4COHORTCited in: Introduction and Definitions of Failure
[13]
Nakajo K, Minamide T, Yamashita H et al.. “Clinical Outcomes and Prognostic Factors in Patients Undergoing Salvage Endoscopic Therapy for cT1N0M0 Local Failure After Chemoradiotherapy for Esophageal Cancer: A Multicenter Retrospective Study.” Digestive endoscopy : official journal of the Japan Gastroenterological Endoscopy Society (2025). PMID: 40931508 ↗
L3COHORTCited in: Introduction and Definitions of Failure
[14]
Wang L, Wang J, Wang T et al.. “Patterns of treatment failure in patients with sinonasal squamous cell carcinoma after chemoradiotherapy.” The British journal of radiology (2024). PMID: 39271160 ↗
L3RETROSPECTIVE_COHORTCited in: Introduction and Definitions of Failure
[15]
Voeten DM, van der Werf LR, Wijnhoven BPL et al.. “Failure to Cure in Patients Undergoing Surgery for Esophageal Carcinoma: Hospital of Surgery Influences Prospects for Cure: A Nation-wide Cohort Study.” Annals of surgery (2020). PMID: 32657922 ↗
L3COHORTCited in: Introduction and Definitions of Failure
[16]
Patel AK, Pan X, Vila DM et al.. “Perineural invasion predicts for locoregional failure in patients with oesophageal adenocarcinoma treated with neoadjuvant chemoradiotherapy.” Journal of clinical pathology (2020). PMID: 32317290 ↗
L3COHORTCited in: Introduction and Definitions of Failure
[17]
Trosman SJ, Zhu A, Nicolli EA et al.. “High-Risk Cutaneous Squamous Cell Cancer of the Head and Neck: Risk Factors for Recurrence and Impact of Adjuvant Treatment.” The Laryngoscope (2020). PMID: 32065413 ↗
L4RETROSPECTIVE_COHORTCited in: Introduction and Definitions of Failure
[18]
Bhattasali O, Ryoo JJ, Thompson LDR et al.. “Impact of chemotherapy regimen on treatment outcomes in patients with HPV-associated oropharyngeal cancer with T4 disease treated with definitive concurrent chemoradiation.” Oral oncology (2019). PMID: 31345397 ↗
L3COHORTCited in: Introduction and Definitions of Failure
[19]
Minamide T, Yoda Y, Hori K et al.. “Advantages of salvage photodynamic therapy using talaporfin sodium for local failure after chemoradiotherapy or radiotherapy for esophageal cancer.” Surgical endoscopy (2019). PMID: 31139985 ↗
L3COHORTCited in: Introduction and Definitions of Failure
[20]
Heukelom J, Navran A, Gouw ZAR et al.. “Organ Function Preservation Failure after (Chemo)Radiotherapy in Head and Neck Cancer: A Retrospective Cohort Analysis.” Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery (2019). PMID: 31060436 ↗
L4RETROSPECTIVE_COHORTCited in: Introduction and Definitions of Failure
[21]
Leong T, Everitt C, Yuen K et al.. “A prospective study to evaluate the impact of FDG-PET on CT-based radiotherapy treatment planning for oesophageal cancer.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2006). PMID: 16545881 ↗
L2NON_RANDOMIZED_TRIALCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[22]
Hsieh CH, Shueng PW, Wang LY et al.. “Single-Institute Clinical Experiences Using Whole-Field Simultaneous Integrated Boost (SIB) Intensity-Modulated Radiotherapy (IMRT) and Sequential IMRT in Postoperative Patients With Oral Cavity Cancer (OCC).” Cancer control : journal of the Moffitt Cancer Center (2020). PMID: 33047615 ↗
L2NON_RANDOMIZED_TRIALCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[23]
Zhou X, Zhu J, Zhou C et al.. “Failure patterns of locoregional recurrence after reducing target volumes in patients with nasopharyngeal carcinoma receiving adaptive replanning during intensity-modulated radiotherapy: a single-center experience in China.” Radiation oncology (London, England) (2023). PMID: 37974274 ↗
L5OTHERCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[24]
Baker S, Verduijn G, Petit S et al.. “Locoregional failures and their relation to radiation fields following stereotactic body radiotherapy boost for oropharyngeal squamous cell carcinoma.” Head & neck (2019). PMID: 30636180 ↗
L5OTHERCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[25]
Chen AM, Chin R, Beron P et al.. “Inadequate target volume delineation and local-regional recurrence after intensity-modulated radiotherapy for human papillomavirus-positive oropharynx cancer.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2017). PMID: 28511960 ↗
L5OTHERCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[26]
Chakraborty S, Patil VM, Babu S et al.. “Locoregional recurrences after post-operative volumetric modulated arc radiotherapy (VMAT) in oral cavity cancers in a resource constrained setting: experience and lessons learned.” The British journal of radiology (2015). PMID: 25645107 ↗
L5OTHERCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[27]
Zheng XK, Chen LH, Wang QS et al.. “Influence of FDG-PET on computed tomography-based radiotherapy planning for locally recurrent nasopharyngeal carcinoma.” International journal of radiation oncology, biology, physics (2007). PMID: 17869450 ↗
L5OTHERCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[28]
Everitt C, Leong T. “Influence of F-fluorodeoxyglucose-positron emission tomography on computed tomography-based radiation treatment planning for oesophageal cancer.” Australasian radiology (2006). PMID: 16732830 ↗
L3COHORTCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[29]
Luo W, Tang YQ, Huang Y et al.. “[Irradiation field design according to locoregional relapse sites after radiotherapy of nasopharyngeal carcinoma].” Ai zheng = Aizheng = Chinese journal of cancer (2006). PMID: 16480588 ↗
L5OTHERCited in: Spatial Patterns: In-field vs. Marginal vs. Out-of-field
[30]
Enke T, Pokala SK, Hensen C et al.. “Recurrent Barrett's esophagus-related neoplasia is uncommon after successful endoscopic eradication therapy over long-term follow-up.” Diseases of the esophagus : official journal of the International Society for Diseases of the Esophagus (2026). PMID: 41758692 ↗
L2PROSPECTIVE_COHORTCited in: Temporal Patterns and Surveillance Timing
[31]
Huang W, Zhang C, Liu W et al.. “Safety of long-term esophageal stent placement and a predictive model for restenosis: A double-center retrospective study.” Surgical endoscopy (2025). PMID: 41466139 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[32]
Fang P, Gunther JR, Pinnix CC et al.. “A Prospective Trial of Radiation Therapy Efficacy and Toxicity for Localized Mucosa-associated Lymphoid Tissue (MALT) Lymphoma.” International journal of radiation oncology, biology, physics (2020). PMID: 33309978 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[33]
Xu S, Li Q, Wang Z et al.. “Evaluating the risk of re-recurrence in patients with persistent/recurrent thyroid carcinoma after initial reoperation.” Surgery (2020). PMID: 33127094 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[34]
Bernardi S, Giudici F, Cesareo R et al.. “Five-Year Results of Radiofrequency and Laser Ablation of Benign Thyroid Nodules: A Multicenter Study from the Italian Minimally Invasive Treatments of the Thyroid Group.” Thyroid : official journal of the American Thyroid Association (2020). PMID: 32578498 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[35]
Soroush A, Poneros JM, Lightdale CJ et al.. “Shorter time to achieve endoscopic eradication is not associated with improved long-term outcomes in Barrett's esophagus.” Diseases of the esophagus : official journal of the International Society for Diseases of the Esophagus (2019). PMID: 30997483 ↗
L3RETROSPECTIVE_COHORTCited in: Temporal Patterns and Surveillance Timing
[36]
de Rienzo-Madero B, Sabra JP, Gand E et al.. “Unilateral benign multinodular versus solitary goiter: Long-term contralateral reoperation rates after lobectomy.” Surgery (2018). PMID: 30415868 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[37]
Zatelli MC, Lamartina L, Meringolo D et al.. “Thyroid nodule recurrence following lobo-isthmectomy: incidence, patient's characteristics, and risk factors.” Journal of endocrinological investigation (2018). PMID: 30182360 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[38]
Virmani P, Jawed S, Myskowski PL et al.. “Long-term follow-up and management of small and medium-sized CD4+ T cell lymphoma and CD8+ lymphoid proliferations of acral sites: a multicenter experience.” International journal of dermatology (2016). PMID: 27369070 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[39]
Chainani-Wu N, Lee D, Madden E et al.. “Clinical predictors of oral leukoplakia recurrence following CO₂ laser vaporization.” Journal of cranio-maxillo-facial surgery : official publication of the European Association for Cranio-Maxillo-Facial Surgery (2015). PMID: 26364762 ↗
L4RETROSPECTIVE_COHORTCited in: Temporal Patterns and Surveillance Timing
[40]
Bachar G, Esmat N, Stern S et al.. “Transarterial embolization for acute head and neck bleeding: eight-year experience with emphasis on rebleeding risk in cancer patients.” The Laryngoscope (2013). PMID: 23494563 ↗
L4RETROSPECTIVE_COHORTCited in: Temporal Patterns and Surveillance Timing
[41]
Ho AS, Tsao GJ, Chen FW et al.. “Impact of positron emission tomography/computed tomography surveillance at 12 and 24 months for detecting head and neck cancer recurrence.” Cancer (2012). PMID: 23225544 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[42]
Mo HY, Sun R, Sun J et al.. “Prognostic value of pretreatment and recovery duration of cranial nerve palsy in nasopharyngeal carcinoma.” Radiation oncology (London, England) (2012). PMID: 22958729 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[43]
Cam A, Shishehbor MH, Bajaj NS et al.. “Outcomes of carotid stenting in patients with previous neck radiation.” Catheterization and cardiovascular interventions : official journal of the Society for Cardiac Angiography & Interventions (2013). PMID: 22887647 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[44]
Blanch JL, Vilaseca I, Bernal-Sprekelsen M et al.. “Prognostic significance of surgical margins in transoral CO2 laser microsurgery for T1-T4 pharyngo-laryngeal cancers.” European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery (2007). PMID: 17479274 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[45]
Kasapoglu F, Erisen L, Coskun H et al.. “Endolaryngeal cordectomy using cold instruments for treatment of T1 glottic cancers.” European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery (2007). PMID: 17431655 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[46]
Taralli S, Lorusso M, Capotosti A et al.. “Which Is the Optimal Scan Time of 18F-DOPA PET/CT in Patients With Recurrent Medullary Thyroid Carcinoma?: Results From a Dynamic Acquisition Study.” Clinical nuclear medicine (2020). PMID: 31977485 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[47]
Ito Y, Miyauchi A, Kihara M et al.. “Prognostic significance of young age in papillary thyroid carcinoma: analysis of 5,733 patients with 150 months' median follow-up.” Endocrine journal (2014). PMID: 24553476 ↗
L3COHORTCited in: Temporal Patterns and Surveillance Timing
[48]
Lee J, Nam KH, Chung WY et al.. “Clinicopathologic features and treatment outcomes in differentiated thyroid carcinoma patients with concurrent Graves' disease.” Journal of Korean medical science (2008). PMID: 18955784 ↗
L4COHORTCited in: Temporal Patterns and Surveillance Timing
[49]
Fakhry C, Zhang Q, Nguyen-Tan PF et al.. “Human papillomavirus and overall survival after progression of oropharyngeal squamous cell carcinoma.” Journal of clinical oncology : official journal of the American Society of Clinical Oncology (2014). PMID: 24958820 ↗
L1RCTCited in: Impact of HPV/p16 Status on Failure Patterns
[50]
Yu Y, Fan D, Song X et al.. “TERT Promoter Mutations Are Enriched in Oral Cavity Cancers and Associated With Locoregional Recurrence.” JCO precision oncology (2021). PMID: 34381934 ↗
L2PROSPECTIVE_COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[51]
Lee NCJ, Kelly JR, Park HS et al.. “Patterns of failure in high-metastatic node number human papillomavirus-positive oropharyngeal carcinoma.” Oral oncology (2018). PMID: 30220317 ↗
L3COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[52]
Burr AR, Harari PM, Ko HC et al.. “Reducing radiotherapy target volume expansion for patients with HPV-associated oropharyngeal cancer.” Oral oncology (2019). PMID: 31010623 ↗
L3COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[53]
Christopherson KM, Moreno AC, Elgohari B et al.. “Outcomes after salvage for HPV-positive recurrent oropharyngeal cancer treated with primary radiation.” Oral oncology (2020). PMID: 33360375 ↗
L3RETROSPECTIVE_COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[54]
Davis KS, Vargo JA, Ferris RL et al.. “Stereotactic body radiotherapy for recurrent oropharyngeal cancer - influence of HPV status and smoking history.” Oral oncology (2014). PMID: 25175942 ↗
L3COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[55]
Sher DJ, Thotakura V, Balboni TA et al.. “Treatment of oropharyngeal squamous cell carcinoma with IMRT: patterns of failure after concurrent chemoradiotherapy and sequential therapy.” Annals of oncology : official journal of the European Society for Medical Oncology (2012). PMID: 22425872 ↗
L4RETROSPECTIVE_COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[56]
Bledsoe TJ, Noble AR, Hunter GK et al.. “Oropharyngeal squamous cell carcinoma with known human papillomavirus status treated with definitive chemoradiotherapy: patterns of failure and toxicity outcomes.” Radiation oncology (London, England) (2013). PMID: 23837872 ↗
L3COHORTCited in: Impact of HPV/p16 Status on Failure Patterns
[57]
Nielsen SB, Kristensen MH, Holm AIS et al.. “Failure pattern and salvage in head and neck cancer of unknown primary: A national study by DAHANCA.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2025). PMID: 41016667 ↗
L5OTHERCited in: Impact of HPV/p16 Status on Failure Patterns
[58]
Yuvnik T, Chia L, Laura OC et al.. “Differences in geometric patterns of failure in human papillomavirus (HPV)-associated and HPV-non-associated oropharyngeal cancer after definitive radiotherapy.” Head & neck (2023). PMID: 38108534 ↗
L5OTHERCited in: Impact of HPV/p16 Status on Failure Patterns
[59]
Holstead R, Rasul R, Golden A et al.. “Identifying patterns of failure and secondary primary malignancies in HPV-related oropharyngeal squamous cell carcinomas.” Future oncology (London, England) (2020). PMID: 31967480 ↗
L5OTHERCited in: Impact of HPV/p16 Status on Failure Patterns
[60]
MacNeil T, Hayman TJ, Li S et al.. “STING predicts patterns of failure in locally advanced head and neck squamous cell carcinoma.” JNCI cancer spectrum (2026). PMID: 41569294 ↗
L5OTHERCited in: Impact of HPV/p16 Status on Failure Patterns
[61]
Cleary RK, Cmelak AJ. “Evolving Treatment Paradigms for Oropharyngeal Squamous Cell Carcinoma.” Journal of global oncology (2016). PMID: 30241193 ↗
L5NARRATIVE_REVIEWCited in: Impact of HPV/p16 Status on Failure Patterns
[62]
Matsuda S, Tsushima T, Kawakubo H et al.. “Safety and efficacy of conversion therapy for metastatic esophageal cancer: exploratory analysis of JCOG1314.” Esophagus : official journal of the Japan Esophageal Society (2025). PMID: 41160311 ↗
L1RCTCited in: Distant Metastasis: Sites and Risk Factors
[63]
Vérillaud B, Chatelet F, Baglin AC et al.. “Sinonasal squamous cell carcinoma: REFCOR guidelines for diagnosis, treatment and follow-up.” European annals of otorhinolaryngology, head and neck diseases (2026). PMID: 42409684 ↗
L1GUIDELINECited in: Distant Metastasis: Sites and Risk Factors
[64]
Sanders ME, van der Horst S, Weijs TJ et al.. “Treatment strategies of esophageal cancer with concurrent cervical node metastasis: a Dutch nationwide population-based cohort study.” Diseases of the esophagus : official journal of the International Society for Diseases of the Esophagus (2026). PMID: 42043275 ↗
L2PROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[65]
Singh S, Varshney VK, Rai A et al.. “Near infrared fluorescence-guided lymphadenectomy during esophagectomy for esophageal squamous cell carcinoma.” Surgery (2026). PMID: 41967430 ↗
L2PROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[66]
Han X, Qi WX, Li SY et al.. “Residual pattern of primary tumor and lymph node in ESCC treated with nCRT with or without pembrolizumab: an analysis from a prospective cohort.” Frontiers in immunology (2025). PMID: 41200162 ↗
L2PROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[67]
Huang SH, Su J, Koyfman SA et al.. “A Proposal for HPV-Associated Oropharyngeal Carcinoma in the Ninth Edition Clinical TNM Classification.” JAMA otolaryngology-- head & neck surgery (2025). PMID: 40338536 ↗
L2NON_RANDOMIZED_TRIALCited in: Distant Metastasis: Sites and Risk Factors
[68]
Nielsen SB, Lyhne NM, Andersen M et al.. “Management of head and neck cancer of unknown primary: A phase IV study by DAHANCA.” European journal of cancer (Oxford, England : 1990) (2024). PMID: 39753047 ↗
L2NON_RANDOMIZED_TRIALCited in: Distant Metastasis: Sites and Risk Factors
[69]
Pourfaraji SM, Jalaeefar A, Ojaghi Shirmard F et al.. “Neuroendocrine carcinoma of esophagus: systematic review and meta-analysis of case series.” BMC gastroenterology (2025). PMID: 40597692 ↗
L4SR_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[70]
Kono M, Sakaue S, Kumai T et al.. “Long-term functional and nutritional outcomes in patients with retropharyngeal lymph node-positive hypopharyngeal cancer treated with concurrent chemoradiotherapy.” Supportive care in cancer : official journal of the Multinational Association of Supportive Care in Cancer (2026). PMID: 42249198 ↗
L4RETROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[71]
Lin ZQ, He CY, He SQ et al.. “Prognostic Value and Therapeutic Implications of MRI-Based Negative Lymph Nodes in Nasopharyngeal Carcinoma.” Cancer medicine (2026). PMID: 42163833 ↗
L3RETROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[72]
Jeon YJ, Son JA, Lee J et al.. “Prognosis of Isolated Cervical Node Recurrence After Esophagectomy With Two-Field Lymphadenectomy for Esophageal Squamous Cell Carcinoma.” The Annals of thoracic surgery (2026). PMID: 41722675 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[73]
Okamura A, Watanabe M, Okui J et al.. “Can combined organ resection cure T4 esophageal cancer? Insights from a multi-institutional study of incomplete resection cases.” Esophagus : official journal of the Japan Esophageal Society (2026). PMID: 41686392 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[74]
Huang SH, Cotler J, Palis B et al.. “Proposed Version Nine of the AJCC and UICC TNM Classification for Salivary Gland Carcinoma.” JAMA otolaryngology-- head & neck surgery (2026). PMID: 41678147 ↗
L3RETROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[75]
Kadota T, Kawachi H, Fujii S et al.. “Long-term outcome after endoscopic resection for esophageal squamous cell carcinoma invading muscularis mucosa without lymphovascular invasion: a multicenter retrospective study.” Gastrointestinal endoscopy (2026). PMID: 41672108 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[76]
Chen SF, Hu YW, Yeh CF et al.. “Association Between Elective Nodal Irradiation and Oncologic Outcomes in Node-Negative Olfactory Neuroblastoma and Sinonasal Squamous Cell Carcinoma: A Propensity-Score Matched Analysis.” Head & neck (2025). PMID: 41467362 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[77]
Gangaram Panday SSG, Pittacolo M, Lagarde SM et al.. “The value of routine endoscopic ultrasound in patients with esophageal cancer undergoing active surveillance after neoadjuvant chemoradiotherapy.” Endoscopy (2025). PMID: 41422800 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[78]
Duan Y, Cheng S, Qin W et al.. “Efficacy and safety of radiotherapy plus immunochemotherapy in patients with oligometastatic esophageal cancer.” Future oncology (London, England) (2025). PMID: 41402130 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[79]
Daoud GE, Burnham AJ, Vettikattu NT et al.. “Minimizing Chemoradiation Using a Surgical Algorithm for HPV-Associated Cancer of Unknown Primary.” Head & neck (2025). PMID: 41355498 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[80]
Koizumi K, Obayashi F, Higaki M et al.. “Postoperative Adjuvant Therapy in Resectable Advanced Oral Squamous Cell Carcinoma With Intermediate Risk Factors.” Head & neck (2025). PMID: 41307158 ↗
L3COHORTCited in: Distant Metastasis: Sites and Risk Factors
[81]
Liu Q, Chen J, Xu Y et al.. “Comparative analysis of immunochemotherapy with versus without radiation therapy for stage IVB esophageal squamous cell carcinoma confined to non-regional nodal metastases: a multicenter propensity score matching study.” Cancer immunology, immunotherapy : CII (2025). PMID: 41251846 ↗
L3RETROSPECTIVE_COHORTCited in: Distant Metastasis: Sites and Risk Factors
[82]
Saksø M, Mortensen LS, Primdahl H et al.. “Influence of FAZA PET hypoxia and HPV-status for the outcome of head and neck squamous cell carcinoma (HNSCC) treated with radiotherapy: Long-term results from the DAHANCA 24 trial (NCT01017224).” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2020). PMID: 32805273 ↗
L4PROSPECTIVE_COHORTCited in: Biological and Molecular Drivers of Resistance
[83]
Jonathan RA, Wijffels KI, Peeters W et al.. “The prognostic value of endogenous hypoxia-related markers for head and neck squamous cell carcinomas treated with ARCON.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2006). PMID: 16730088 ↗
L2NON_RANDOMIZED_TRIALCited in: Biological and Molecular Drivers of Resistance
[84]
Marcu LG, Reid P, Bezak E. “The Promise of Novel Biomarkers for Head and Neck Cancer from an Imaging Perspective.” International journal of molecular sciences (2018). PMID: 30149561 ↗
L5NARRATIVE_REVIEWCited in: Biological and Molecular Drivers of Resistance
[85]
Sugiura K, Nakajima S, Kato I et al.. “Hypoxia and CD11b+ Cell Influx Are Strongly Associated With Lymph Node Metastasis of Oral Cancer.” Anticancer research (2020). PMID: 33288576 ↗
L5OTHERCited in: Biological and Molecular Drivers of Resistance
[86]
Xie L, Zhang K, You B et al.. “Hypoxic nasopharyngeal carcinoma-derived exosomal miR-455 increases vascular permeability by targeting ZO-1 to promote metastasis.” Molecular carcinogenesis (2023). PMID: 36929868 ↗
L5OTHERCited in: Biological and Molecular Drivers of Resistance
[87]
Yang H, Chen X, Lin S et al.. “Treatment outcomes after reduction of the target volume of intensity-modulated radiotherapy following induction chemotherapy in patients with locoregionally advanced nasopharyngeal carcinoma: A prospective, multi-center, randomized clinical trial.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2017). PMID: 28864073 ↗
L1RCTCited in: Technical Factors Influencing Failure
[88]
Vanderveken OM, Szturz P, Specenier P et al.. “Gemcitabine-Based Chemoradiation in the Treatment of Locally Advanced Head and Neck Cancer: Systematic Review of Literature and Meta-Analysis.” The oncologist (2015). PMID: 26712958 ↗
L2SR_COHORTCited in: Technical Factors Influencing Failure
[89]
Tsai WL, Huang YJ, Fang FM. “Biophysical Skin Response in Head and Neck Cancer: Longitudinal Comparison of Modern Photon and Proton Radiotherapy.” The Journal of dermatology (2026). PMID: 41531419 ↗
L2PROSPECTIVE_COHORTCited in: Technical Factors Influencing Failure
[90]
Sommat K, Hussain A, Ong WS et al.. “Clinical and dosimetric predictors of physician and patient reported xerostomia following intensity modulated radiotherapy for nasopharyngeal cancer - A prospective cohort analysis.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2019). PMID: 31265972 ↗
L2PROSPECTIVE_COHORTCited in: Technical Factors Influencing Failure
[91]
Söderström K, Nilsson P, Dalianis T et al.. “Regional recurrence of oropharyngeal cancer after definitive radiotherapy: a case control study.” Radiation oncology (London, England) (2015). PMID: 26014350 ↗
L2PROSPECTIVE_COHORTCited in: Technical Factors Influencing Failure
[92]
Santos M, Oliveira E Silva LF, Kohler HF et al.. “Health-Related Quality of Life Outcomes in Head and Neck Cancer: Results From a Prospective, Real-World Data Study With Brazilian Patients Treated With Intensity Modulated Radiation Therapy, Conformal and Conventional Radiation Techniques.” International journal of radiation oncology, biology, physics (2020). PMID: 33007435 ↗
L2NON_RANDOMIZED_TRIALCited in: Technical Factors Influencing Failure
[93]
Mavroidis P, Price A, Fried D et al.. “Dose-volume toxicity modeling for de-intensified chemo-radiation therapy for HPV-positive oropharynx cancer.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2017). PMID: 28712533 ↗
L2NON_RANDOMIZED_TRIALCited in: Technical Factors Influencing Failure
[94]
Fei Z, Xu T, Qiu X et al.. “Significance of boost dose for T4 nasopharyngeal carcinoma with residual primary lesion after intensity-modulated radiotherapy.” Journal of cancer research and clinical oncology (2021). PMID: 33392660 ↗
L3RETROSPECTIVE_COHORTCited in: Technical Factors Influencing Failure
[95]
Lu T, Xie X, Guo Q et al.. “Prognosis of nasopharyngeal carcinoma with insufficient radical dose to the primary site in the intensity-modulated radiotherapy era.” Head & neck (2019). PMID: 31313419 ↗
L4COHORTCited in: Technical Factors Influencing Failure
[96]
Vallard A, Guy JB, Mengue Ndong S et al.. “Intensity-modulated radiotherapy or volumetric-modulated arc therapy in patients with head and neck cancer: Focus on salivary glands dosimetry.” Head & neck (2016). PMID: 26855006 ↗
L3COHORTCited in: Technical Factors Influencing Failure
[97]
Messer JA, Mohamed AS, Hutcheson KA et al.. “Magnetic resonance imaging of swallowing-related structures in nasopharyngeal carcinoma patients receiving IMRT: Longitudinal dose-response characterization of quantitative signal kinetics.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2016). PMID: 26830697 ↗
L3COHORTCited in: Technical Factors Influencing Failure
[98]
Al-Mamgani A, Kwa SL, Tans L et al.. “Single Vocal Cord Irradiation: Image Guided Intensity Modulated Hypofractionated Radiation Therapy for T1a Glottic Cancer: Early Clinical Results.” International journal of radiation oncology, biology, physics (2015). PMID: 26264629 ↗
L4COHORTCited in: Technical Factors Influencing Failure
[99]
. “Dose-volume correlates of mandibular osteoradionecrosis in Oropharynx cancer patients receiving intensity-modulated radiotherapy: Results from a case-matched comparison.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2017). PMID: 28733053 ↗
L4CASE_CONTROLCited in: Technical Factors Influencing Failure
[100]
Alterio D, D'Ippolito E, Vischioni B et al.. “Mixed-beam approach in locally advanced nasopharyngeal carcinoma: IMRT followed by proton therapy boost versus IMRT-only. Evaluation of toxicity and efficacy.” Acta oncologica (Stockholm, Sweden) (2020). PMID: 32090645 ↗
L2NON_RANDOMIZED_TRIALCited in: Technical Factors Influencing Failure
[101]
Xue F, Hu C, He X. “Impact of minimum point dose on local control and toxicity in T3-4 nasopharyngeal carcinoma treated with intensity-modulated radiation therapy plus chemotherapy.” Japanese journal of clinical oncology (2018). PMID: 29294009 ↗
L2NON_RANDOMIZED_TRIALCited in: Technical Factors Influencing Failure
[102]
Zhang SM, Li FY, Hao MY et al.. “Dose-dependent taste dysfunction in head and neck cancer patients receiving radiotherapy.” Radiation oncology (London, England) (2025). PMID: 41345943 ↗
L3CROSS_SECTIONALCited in: Technical Factors Influencing Failure
[103]
Schmitt NC, Stokes WA, Bates JE et al.. “Early-Phase Trial of IAP Antagonist Tolinapant and Definitive Radiation in Cisplatin-Ineligible Patients with Advanced Head and Neck Cancer.” Clinical cancer research : an official journal of the American Association for Cancer Research (2025). PMID: 40353748 ↗
L4PHASE_1_TRIALCited in: Technical Factors Influencing Failure
[104]
Rooney KP, Miah AB, Bhide SA et al.. “Intensity modulated radiotherapy in locally advanced thyroid cancer: Outcomes of a sequential phase I dose-escalation study.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2018). PMID: 29525412 ↗
L4PHASE_1_TRIALCited in: Technical Factors Influencing Failure
[105]
Chen R, Chen J, Liu X et al.. “VMAT with CCC Algorithm Optimizes Trismus Prevention: Dose-Response Analysis of Jaw Muscles Dmean and Dmax in T3-T4 Nasopharyngeal Carcinoma.” Technology in cancer research & treatment (2025). PMID: 41166228 ↗
L3RETROSPECTIVE_COHORTCited in: Technical Factors Influencing Failure
[106]
Inoue E, Okajima K, Doi H et al.. “Factors predictive of the development of hypothyroidism after intensity-modulated radiation therapy for pharyngeal cancer.” Acta oto-laryngologica (2021). PMID: 34738883 ↗
L4COHORTCited in: Technical Factors Influencing Failure
[107]
Williamson A, Brady G, Harris N et al.. “Multidisciplinary evidence-based consensus statements on salvage surgery for recurrent head and neck cancer (International Centre for Recurrent Head and Neck Cancer).” Journal of the National Cancer Institute (2025). PMID: 40515663 ↗
L1GUIDELINECited in: Salvage Options and Outcomes After Failure
[108]
Sasaki K, Nomura M, Kato K et al.. “A phase III randomized controlled trial comparing local field with additional prophylactic irradiation in chemoradiotherapy for clinical-T1bN0M0 esophageal cancer: ARMADILLO trial (JCOG1904).” Japanese journal of clinical oncology (2024). PMID: 37801434 ↗
L1RCTCited in: Salvage Options and Outcomes After Failure
[109]
An PG, Zhang J, Hu X et al.. “Preoperative Chemoimmunotherapy Followed by Salvage Surgery and Adjuvant Tislelizumab for Previously Irradiated Recurrent HNSCC: A Prospective Phase II Trial.” Clinical cancer research : an official journal of the American Association for Cancer Research (2026). PMID: 41941265 ↗
L2NON_RANDOMIZED_TRIALCited in: Salvage Options and Outcomes After Failure
[110]
Yang KL, Chi MS, Hao CY et al.. “Phase II clinical trial assessing the addition of hyperthermia to salvage concurrent chemoradiotherapy for unresectable recurrent head and neck cancer in previously irradiated patients.” Radiation oncology (London, England) (2025). PMID: 39920700 ↗
L2NON_RANDOMIZED_TRIALCited in: Salvage Options and Outcomes After Failure
[111]
Laxague F, Zabihi-Pour D, Correa Roa CC et al.. “Transoral Robotic Surgery (TORS) Versus Open Surgery for Recurrent Oropharyngeal Squamous Cell Carcinoma: A Systematic Review and Meta-Analysis.” Head & neck (2025). PMID: 40927878 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[112]
Goel S, Gunasekera D, Krishnan G et al.. “Is transoral robotic surgery useful as a salvage technique in head and neck cancers: a systematic review and meta analysis.” Head & neck (2024). PMID: 39737644 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[113]
Bozkurt G, Turri Zanoni M, Ferrari M et al.. “Salvage surgery in nasopharyngeal Cancer: Unraveling the efficacy of transnasal endoscopic nasopharyngectomy for advanced stage recurrent tumors.” Oral oncology (2024). PMID: 39362026 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[114]
Lee OH, Bang J, Kim GJ et al.. “Clinical outcome of salvage surgery in patients with recurrent oral cavity cancer: A systematic review and meta-analysis.” Head & neck (2024). PMID: 39243149 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[115]
Cooke PV, Wu MP, Rathi VK et al.. “Salvage surgery for recurrent or residual hypopharyngeal squamous cell carcinoma: A systematic review.” Head & neck (2024). PMID: 38716810 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[116]
Saturno M, Shaari AL, Yun J et al.. “Outcomes of Supracricoid Partial Laryngectomy Performed in the United States: A Systematic Review.” The Laryngoscope (2024). PMID: 38251796 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[117]
Williamson A, Jashek-Ahmed F, Hardman J et al.. “Functional and quality-of-life outcomes following salvage surgery for recurrent squamous cell carcinoma of the head and neck: a systematic review and meta-analysis.” European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery (2023). PMID: 37329358 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[118]
Wang D, Liao M, Wu J et al.. “Salvage treatments for locally recurrent nasopharyngeal cancer: Systematic review and meta-analysis.” Head & neck (2022). PMID: 36420965 ↗
L2SR_COHORTCited in: Salvage Options and Outcomes After Failure
[119]
Abdulrahman R, Kharytaniuk N, Birido N et al.. “Salvage surgery for oesophageal cancer: The need for more intensive surveillance.” European journal of surgical oncology : the journal of the European Society of Surgical Oncology and the British Association of Surgical Oncology (2024). PMID: 39765194 ↗
L2PROSPECTIVE_COHORTCited in: Salvage Options and Outcomes After Failure
[120]
Williamson A, Burton S, Rajan Z et al.. “Salvage surgery for residual and recurrent head and neck squamous cell carcinoma (RESCUE): An IReC multicentre consecutive cohort study.” Oral oncology (2026). PMID: 42208312 ↗
L3RETROSPECTIVE_COHORTCited in: Salvage Options and Outcomes After Failure
[121]
Pansa A, Di Benedetto M, Giorgi L et al.. “Minimally invasive total pharyngo-laryngo-esophagectomy as a salvage procedure, technical notes and outcomes from a multidisciplinary team approach.” Updates in surgery (2026). PMID: 41758289 ↗
L4COHORTCited in: Salvage Options and Outcomes After Failure
[122]
Holgado A, Llansana A, Vázquez C et al.. “Identification of prognostic variables in patients with recurrent head and neck squamous cell carcinoma treated with salvage surgery: Implications for treatment with immunotherapy.” Oral oncology (2026). PMID: 41722172 ↗
L3RETROSPECTIVE_COHORTCited in: Salvage Options and Outcomes After Failure
[123]
Luo Y, Cai B, Li B et al.. “Safety and Efficacy of Salvage Treatment for Recurrent Nasopharyngeal Carcinoma: A Single-Center Retrospective Study Over 10 Years.” Cancer medicine (2026). PMID: 41692431 ↗
L3COHORTCited in: Salvage Options and Outcomes After Failure
[124]
Saykaly J, Vergez S, Dupret-Bories A et al.. “Oncological Outcomes of Salvage Oropharyngectomy in Irradiated Neck for Recurrent or Metachronous Squamous Cell Carcinoma.” Head & neck (2026). PMID: 41612947 ↗
L4COHORTCited in: Salvage Options and Outcomes After Failure
[125]
Elaprolu S, Sunny SP, Menon LR et al.. “Machine learning to predict complications after salvage surgery in head and neck cancers.” International journal of oral and maxillofacial surgery (2025). PMID: 41253618 ↗
L3COHORTCited in: Salvage Options and Outcomes After Failure
[126]
Yamauchi M, Sakai A, Ebisumoto K et al.. “Evaluating Clinical Outcomes and Predictive Factors of Treatment Approaches in T1-3N3b Hypopharyngeal Carcinoma: Upfront Neck Dissection Versus Concurrent Chemoradiotherapy.” Head & neck (2025). PMID: 40718935 ↗
L4COHORTCited in: Salvage Options and Outcomes After Failure
[127]
Bourhis J, Aupérin A, Borel C et al.. “Nivolumab added to cisplatin and radiotherapy versus cisplatin and radiotherapy alone after surgery for people with squamous cell carcinoma of the head and neck at a high risk of relapse (GORTEC 2018-01 NIVOPOST-OP): a randomised, open-label, phase 3 trial.” Lancet (London, England) (2025). PMID: 41448222 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[128]
Bourhis J, Sire C, Graff P et al.. “Concomitant chemoradiotherapy versus acceleration of radiotherapy with or without concomitant chemotherapy in locally advanced head and neck carcinoma (GORTEC 99-02): an open-label phase 3 randomised trial.” The Lancet. Oncology (2012). PMID: 22261362 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[129]
Janoray G, Pointreau Y, Garaud P et al.. “Long-term Results of a Multicenter Randomized Phase III Trial of Induction Chemotherapy With Cisplatin, 5-fluorouracil, ± Docetaxel for Larynx Preservation.” Journal of the National Cancer Institute (2015). PMID: 26681800 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[130]
Caudell JJ, Torres-Saavedra PA, Rosenthal DI et al.. “Long-Term Update of NRG/RTOG 0522: A Randomized Phase 3 Trial of Concurrent Radiation and Cisplatin With or Without Cetuximab in Locoregionally Advanced Head and Neck Cancer.” International journal of radiation oncology, biology, physics (2022). PMID: 36549347 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[131]
Ang KK, Zhang Q, Rosenthal DI et al.. “Randomized phase III trial of concurrent accelerated radiation plus cisplatin with or without cetuximab for stage III to IV head and neck carcinoma: RTOG 0522.” Journal of clinical oncology : official journal of the American Society of Clinical Oncology (2014). PMID: 25154822 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[132]
Fakhry C, Zhang Q, Gillison ML et al.. “Validation of NRG oncology/RTOG-0129 risk groups for HPV-positive and HPV-negative oropharyngeal squamous cell cancer: Implications for risk-based therapeutic intensity trials.” Cancer (2019). PMID: 30913305 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[133]
Xiao C, Hanlon A, Zhang Q et al.. “Risk factors for clinician-reported symptom clusters in patients with advanced head and neck cancer in a phase 3 randomized clinical trial: RTOG 0129.” Cancer (2013). PMID: 24338990 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[134]
Xiao C, Zhang Q, Nguyen-Tân PF et al.. “Quality of Life and Performance Status From a Substudy Conducted Within a Prospective Phase 3 Randomized Trial of Concurrent Standard Radiation Versus Accelerated Radiation Plus Cisplatin for Locally Advanced Head and Neck Carcinoma: NRG Oncology RTOG 0129.” International journal of radiation oncology, biology, physics (2016). PMID: 27727063 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[135]
Eriksen JG, Maare C, Johansen J et al.. “DAHANCA19: A randomized phase III study of primary curative (chemo)-radiotherapy and the EGFR-inhibitor zalutumumab for squamous cell carcinoma of the head and neck.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2025). PMID: 40258418 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[136]
Racadot S, Thennevet I, Ouldbey Y et al.. “Afatinib maintenance therapy following post-operative radiochemotherapy in head and neck squamous cell carcinoma: Results from the phase III randomised double-blind placebo-controlled study BIB2992ORL (GORTEC 2010-02).” European journal of cancer (Oxford, England : 1990) (2022). PMID: 36434888 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[137]
Tao Y, Aupérin A, Sun X et al.. “Avelumab-cetuximab-radiotherapy versus standards of care in locally advanced squamous-cell carcinoma of the head and neck: The safety phase of a randomised phase III trial GORTEC 2017-01 (REACH).” European journal of cancer (Oxford, England : 1990) (2020). PMID: 33125944 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[138]
Tao Y, Aupérin A, Graff P et al.. “Very accelerated radiotherapy or concurrent chemoradiotherapy for N3 head and neck squamous cell carcinoma: Pooled analysis of two GORTEC randomized trials.” Oral oncology (2017). PMID: 28688693 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[139]
Wuthrick EJ, Zhang Q, Machtay M et al.. “Institutional clinical trial accrual volume and survival of patients with head and neck cancer.” Journal of clinical oncology : official journal of the American Society of Clinical Oncology (2014). PMID: 25488965 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[140]
Lyhne NM, Primdahl H, Kristensen CA et al.. “The DAHANCA 6 randomized trial: Effect of 6 vs 5 weekly fractions of radiotherapy in patients with glottic squamous cell carcinoma.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2015). PMID: 26255764 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[141]
Bourhis J, Lapeyre M, Tortochaux J et al.. “Phase III randomized trial of very accelerated radiation therapy compared with conventional radiation therapy in squamous cell head and neck cancer: a GORTEC trial.” Journal of clinical oncology : official journal of the American Society of Clinical Oncology (2006). PMID: 16782926 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[142]
Hansen CR, Samsøe E, Smulders B et al.. “Radiotherapy quality assurance of patients with squamous cell carcinoma of the head and neck included in the DAHANCA 19 randomised phase III trial.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2025). PMID: 40825443 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[143]
Tao Y, Auperin A, Blanchard P et al.. “Concurrent cisplatin and dose escalation with intensity-modulated radiotherapy (IMRT) versus conventional radiotherapy for locally advanced head and neck squamous cell carcinomas (HNSCC): GORTEC 2004-01 randomized phase III trial.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2020). PMID: 32417348 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[144]
Frikha M, Auperin A, Tao Y et al.. “A randomized trial of induction docetaxel-cisplatin-5FU followed by concomitant cisplatin-RT versus concomitant cisplatin-RT in nasopharyngeal carcinoma (GORTEC 2006-02).” Annals of oncology : official journal of the European Society for Medical Oncology (2018). PMID: 29236943 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[145]
Overgaard J, Hoff CM, Hansen HS et al.. “DAHANCA 10 - Effect of darbepoetin alfa and radiotherapy in the treatment of squamous cell carcinoma of the head and neck. A multicenter, open-label, randomized, phase 3 trial by the Danish head and neck cancer group.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2018). PMID: 29523409 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[146]
Lønbro S, Dalgas U, Primdahl H et al.. “Progressive resistance training rebuilds lean body mass in head and neck cancer patients after radiotherapy--results from the randomized DAHANCA 25B trial.” Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology (2013). PMID: 23932192 ↗
L1RCTCited in: Landmark Trials Reporting Failure Patterns
[147]
Ardila CM, Pineda-Vélez E, Vivares-Builes AM et al.. “MRI-Based Radiomics and Artificial Intelligence for Prediction of Recurrence and Prognostic Outcomes in Oral Tongue Squamous Cell Carcinoma: A Systematic Review with Functional Meta-Synthesis.” Medical sciences (Basel, Switzerland) (2026). PMID: 42346871 ↗
L2SR_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[148]
Ardila CM, Pineda-Vélez E, Vivares-Builes AM et al.. “Artificial-Intelligence-Based Radiologic, Histopathologic, and Molecular Models for the Diagnosis and Classification of Malignant Salivary Gland Tumors: A Systematic Review and Functional Meta-Synthesis.” Medical sciences (Basel, Switzerland) (2026). PMID: 42029607 ↗
L4SR_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[149]
Singh SP, Prasad S, Dean PM et al.. “Prognostic significance of extranodal extension in cervical lymph node metastases of head and neck squamous cell carcinoma: A systematic review and meta-analysis with bibliometric overview.” Oral oncology (2026). PMID: 41655423 ↗
L2SR_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[150]
Zhao F, Liu J, Ling J et al.. “Could a multimodal fusion model integrating CT radiomics and systemic inflammatory markers improve preoperative risk stratification of parotid masses? A retrospective exploratory study.” Frontiers in immunology (2026). PMID: 42459681 ↗
L2PROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[151]
Lu W, Zhang D, Wu X et al.. “An online nomogram based on bimodal ultrasound images for preoperative diagnosis of cytologically indeterminate thyroid nodules.” Frontiers in endocrinology (2026). PMID: 42445878 ↗
L2PROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[152]
Barioni ED, Orhan K, Borges-Oliveira AC et al.. “Multimodal Radiogenomic Imaging in Oropharyngeal Squamous Cell Carcinoma: Implications for Dentomaxillofacial Radiology.” Medical sciences (Basel, Switzerland) (2026). PMID: 42029598 ↗
L2PROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[153]
Nabavizadeh SS, Safari F, Mehrian SRA et al.. “Diagnostic Accuracy of Ultrasound Radiomics for Cervical Lymph-Node Metastasis in Papillary Thyroid Carcinoma: Evidence Predominantly From Chinese Cohorts.” Ultrasound in medicine & biology (2026). PMID: 41997788 ↗
L2SR_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[154]
Jazi SS, Khademi M, Abedi I et al.. “Advances in radiomics for predicting and managing xerostomia following radiotherapy: A systematic review.” Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB) (2026). PMID: 41628580 ↗
L2SR_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[155]
Li S, Zhou Y, Li W et al.. “Development and validation of an intra-tumoral and peri-tumoral radiomics model based on dynamic contrast-enhanced ultrasound for predicting lymph node metastasis in type 2 diabetic patients with thyroid cancer.” Frontiers in endocrinology (2026). PMID: 42416904 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[156]
Ding L, Wu J, Liang Y et al.. “MRI-Based DeltaHabitat Radiomic Model Predicts Pathological Complete Response in Oral Cavity Cancer Treated With Neoadjuvant Chemoimmunotherapy.” Cancer medicine (2026). PMID: 42298309 ↗
L4RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[157]
He S, Lyu GR, Cai M et al.. “Super-resolution ultrasound radiomics for pre-FNA prediction of nondiagnostic (Bethesda I) thyroid nodules.” Frontiers in endocrinology (2026). PMID: 42147094 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[158]
Yao Y, Zhao Y, Yuan Q et al.. “Prediction of recurrent laryngeal nerve lymph node metastasis in esophageal squamous cell carcinoma based on CT radiomics model: A multicenter study.” European journal of surgical oncology : the journal of the European Society of Surgical Oncology and the British Association of Surgical Oncology (2026). PMID: 42107168 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[159]
Yao J, Wang D, Pu KM et al.. “A multimodal study on predicting extrathyroidal extension of papillary thyroid carcinoma based on radiopathomics.” BMC endocrine disorders (2026). PMID: 42104301 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[160]
Wen H, Liu XR, Peng XJ et al.. “Tumor subregion-based CT habitat radiomics to improve prediction of nodal disease in esophageal squamous cell carcinoma.” European journal of radiology (2026). PMID: 42097070 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[161]
Peng X, Zhang J, Lin Y et al.. “Predicting central lymph node metastasis in papillary thyroid microcarcinoma: a study of ultrasound and clinical features.” Frontiers in endocrinology (2026). PMID: 42039136 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[162]
Samson DO, Ismail M, Hanifa MAM et al.. “SHAP-based interpretable machine learning with longitudinal delta-radiomics across seven weeks of treatment for xerostomia prediction in head-and-neck cancer.” Radiation oncology (London, England) (2026). PMID: 42026673 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[163]
Wen J, Chen Q, Luo L et al.. “Region-guided decoupled fusion network for ultrasound-based classification of thyroid nodules with and without Hashimoto's thyroiditis.” European journal of radiology (2026). PMID: 41996838 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[164]
Wang R, Ren J, Zhang Y et al.. “An Interpretable Machine Learning Model With Synthetic MRI-Based Habitat Radiomics for Predicting Lymph Node Metastasis in Oral Cancer.” Cancer medicine (2026). PMID: 41992656 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[165]
Benyoucef R, Goubet M, Barrat A et al.. “Do MRI radiomic models truly generalize? External validation of three studies in parotid lesion characterization.” European radiology (2026). PMID: 41944835 ↗
L3COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics
[166]
Stoiber S, Pölöske D, Spielvogel CP et al.. “[18F]FDG PET/CT multiomics identifies Hedgehog-driven HPV-negative head and neck squamous cell carcinoma.” Molecular cancer (2026). PMID: 41904511 ↗
L3RETROSPECTIVE_COHORTCited in: Future Directions: Adaptive Radiotherapy and Radiomics