Peptides›Sexual / hormonal›Tamoxifen

Tamoxifen

/ Selective estrogen receptor modulator (SERM); triphenylethylene class

TIER 1 · ClinicalN = 0 · TESTING PENDINGMW 371.50 g·mol⁻¹

ALIAS · Nolvadex (trade) · Tamoxifen citrate

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Research use onlyAny dose figures below describe what specific cited studies used, reported factually. Nothing on this page is guidance for human use.READ FIRST →

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§ A · Identity

Primary sequence— sequence not captured —

MW · 371.50CLASS · Selective estrogen receptor modulator (SERM); triphenylethylene classCATEGORY · Sexual / hormonal

Tier 1. FDA-approved 1977 for breast cancer treatment; subsequently approved for adjuvant treatment of node-positive and node-negative ER-positive breast cancer, ductal carcinoma in situ, and (1998) reduction of breast cancer incidence in high-risk women (BCPT). One of the most-studied drugs in oncology with decades of trial and post-marketing data.

§ B · Mechanism of action

Tamoxifen and its active metabolite 4-hydroxytamoxifen and endoxifen bind the estrogen receptor with tissue-selective effects: antagonist in breast tissue (reduces growth signalling in ER-positive breast cancer cells), partial agonist in bone (preserves BMD), agonist in endometrium (increases endometrial cancer risk), partial agonist on coagulation (increases thromboembolism risk).

§ C · Human clinical evidence

Tier 1. EBCTCG meta-analyses establish 5-year adjuvant tamoxifen reduces 15-year breast cancer mortality by approximately one-third in ER-positive disease. NSABP P-1 (Fisher 1998) established efficacy in chemoprevention.

§ D · Primary literature

PubMed9747868Fisher B et al. — Tamoxifen for prevention of breast cancer: report of the National Surgical Adjuvant Breast and Bowel Project P-1 Study · Journal of the National Cancer Institute · human-phase-3-rctTamoxifen 20 mg/day for five years reduced invasive breast cancer incidence by 49% in women at increased risk; foundational trial for chemoprevention indication.Limitations: Increased endometrial cancer and thromboembolic events; risk-benefit balance most favourable in highest-risk subgroups.1998

PubMed21802721EBCTCG et al. — Relevance of breast cancer hormone receptors and other factors to the efficacy of adjuvant tamoxifen: patient-level meta-analysis of randomised trials · The Lancet · meta-analysisPatient-level meta-analysis of 20 trials confirmed 5 years of adjuvant tamoxifen reduces 15-year breast cancer mortality by approximately one-third in ER-positive disease.Limitations: Older trials used heterogeneous dosing and follow-up; ER-negative tumours derived no benefit.2011

PubMed23219286Davies C et al. — Long-term effects of continuing adjuvant tamoxifen to 10 years versus stopping at 5 years after diagnosis of oestrogen receptor-positive breast cancer: ATLAS, a randomised trial · The Lancet · human-phase-3-rctContinuing tamoxifen to 10 years reduced breast cancer recurrence and mortality compared with stopping at 5 years in ER-positive disease (ATLAS).Limitations: Increased absolute risk of endometrial cancer and pulmonary embolism on extended therapy.2013

§ F · Safety signal

Increased risk of endometrial cancer and venous thromboembolism are the established class concerns. Hot flashes, night sweats, mood changes, and vaginal dryness are common.

§ H · Regulatory status

Regulatory status

FDA status:: FDA-approved
Compounding:: Not eligible for compounding (approved, not in shortage)

§ I · Notable gaps and controversies

The 'PCT' (post-cycle therapy) use case promoted in vendor channels — tamoxifen as estrogen-receptor blockade after exogenous androgenic-anabolic steroid use — does not have controlled-trial support of the kind that underlies the oncology approvals. Liver, thrombotic, and ER-blockade-axis concerns of the SERM class apply regardless of indication.