{"entity":{"id":"tamoxifen","kind":"drug","name":"Tamoxifen","aka":[],"tldr":"The original targeted cancer drug (1977): a pill that blocks oestrogen's effect on breast cancer and halves recurrence, still essential for premenopausal women.","summary":"Selective oestrogen receptor modulator: antagonist in breast, partial agonist in bone and endometrium. Five years reduces 15-year breast cancer mortality by about a third (EBCTCG); ten years is better than five (ATLAS, aTTom). Standard for premenopausal women (alone or with OFS), for men, and for chemoprevention. Endometrial cancer and thromboembolism are the serious rare harms; CYP2D6 activation to endoxifen.","status":"approved","asOf":"2026-09-07","wikipedia":"https://en.wikipedia.org/wiki/Tamoxifen","links":[{"label":"FDA label (DailyMed)","url":"https://dailymed.nlm.nih.gov/dailymed/search.cfm?query=Tamoxifen"}],"tags":[],"related":[],"cancers":["breast-hr-positive"],"sections":[],"technologies":["endocrine-therapy","chemoprevention"],"targets":["estrogen-receptor"],"drugs":[],"companies":["astrazeneca"],"institutions":[],"pathways":[],"terms":[],"trials":["soft-text","dbcg-82bc","nct05768139","nct06979596","nct05774951","nct04906395","nct07287098","nct06492616","nct02747004","nct05514054"],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"brand":"Nolvadex","modality":"Small-molecule SERM","mechanism":"Competitive ER antagonist in breast tissue; tissue-selective co-regulator recruitment.","approvals":[{"region":"US","year":1977,"indication":"Advanced breast cancer"},{"region":"US","year":1998,"indication":"Risk reduction in high-risk women"}],"mechanismSteps":["Tamoxifen is converted by CYP2D6 to endoxifen","Endoxifen binds the ER ligand pocket","Co-repressors rather than co-activators are recruited in breast cells","ER-driven genes (cyclin D1, PGR) are silenced","Proliferation stops; bone and endometrium see partial agonism"],"dosing":{"route":"Oral","schedule":"20 mg once daily for 5-10 years","modifications":"Low-dose 5 mg for DCIS/prevention (TAM-01)","monitoring":"Gynaecologic symptoms; avoid strong CYP2D6 inhibitors"},"toxicity":[{"event":"Hot flushes","anyGradePct":41},{"event":"Endometrial cancer (10-year cumulative)","anyGradePct":3},{"event":"Venous thromboembolism","anyGradePct":2},{"event":"Cataract","anyGradePct":5}],"access":[],"regulatoryEvents":[]},"route":"/drugs/tamoxifen/","neighbours":{"cancer":[{"id":"ductal-carcinoma-in-situ","kind":"cancer","name":"Ductal carcinoma in situ 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