Endocrine Biomarker Changes in a Randomised Low-Dose Tamoxifen Trial for Breast Cancer Prevention
In brief
Low-dose tamoxifen produces dose-dependent rise in SHBG levels
In the KARISMA trial of 1,055 healthy women, six months of tamoxifen at 1 to 20 mg daily increased sex-hormone-binding globulin, with higher doses giving larger rises and modest effects on cortisol and hydroxyprogesterone. These endocrine shifts suggest low-dose regimens have measurable biological activity, but clinical relevance for breast-cancer prevention remains to be defined.
- Journal
- Journal of the National Cancer Institute (Q1)
- Published
- 10 September 2026
- Study design
- Randomized controlled trial
- Evidence level
- Level 1, High (CEBM 1b)
- Authors
- Stephen Nash, Mattias Hammarström, John-Olof Thörngen, Ola Winqvist, Erik Eliasson, Magnus Bäcklund, et al.
- PMID
- 42720596
- DOI
- 10.1093/jnci/djag321
Why clinicians should know about it
- Picked for Biochemistry (medical) (paper of the day, 12 September 2026): Endocrine biomarker changes in low‑dose tamoxifen trial
Abstract
BACKGROUND: Tamoxifen reduces breast cancer incidence and recurrence, but uptake for primary prevention remains limited, largely because of concerns regarding adverse effects at the standard 20 mg dose. Understanding systemic endocrine effects of lower tamoxifen doses may help improve future prevention strategies. METHODS: We analysed data from 1,055 healthy women enrolled in the randomised, double-blind, placebo-controlled KARISMA trial, assigned to placebo or tamoxifen 1, 2.5, 5, 10, or 20 mg daily for 6 months. Plasma concentrations of endocrine biomarkers and tamoxifen metabolites were measured at study end. Associations between randomised tamoxifen dose, circulating metabolite concentrations, and endocrine biomarker plasma concentration (estrogens, androgens, progestogens, cortisol, prolactin, and sex hormone-binding globulin (SHBG)), were evaluated. RESULTS: Tamoxifen dose was associated with measurable endocrine changes after six months, most consistently increased SHBG levels, with additional associations observed for cortisol and hydroxyprogesterone. SHBG demonstrated the clearest dose-response relationship, with increasing levels across tamoxifen dose groups and evidence of attenuated increase at intermediate doses. Large relative differences between placebo and 20 mg tamoxifen were additionally observed for estrone, estrone sulphate and estradiol. Unadjusted analyses of circulating endoxifen showed broadly similar endocrine patterns; however, these associations were substantially attenuated after adjustment for randomised tamoxifen dose. Circulating tamoxifen metabolites were strongly correlated with administered dose and with one another. CONCLUSIONS: Low-dose tamoxifen was associated with measurable endocrine changes, particularly in SHBG, cortisol, and hydroxyprogesterone. These findings show endocrine pharmacodynamic responses during low-dose tamoxifen therapy warrants further investigation as a potential component of future individualised prevention and adjuvant endocrine therapy strategies. TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT03346200.
Abstract as published, via PubMed.
For healthcare professionals. The summary is generated by AI from the published abstract, and the evidence level is assigned automatically from the study design on the Oxford CEBM hierarchy. Neither is medical advice. Read the full paper before changing practice.