# Tamoxifen

Source: https://onco.cc/drugs/tamoxifen/  
OnCo record `tamoxifen` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

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.

## Fields

- Kind: Treatment
- Status: approved
- Last checked: 2026-09-07
- Brand: Nolvadex
- Modality: Small-molecule SERM
- Mechanism: Competitive ER antagonist in breast tissue; tissue-selective co-regulator recruitment.
- Approvals: US 1977: Advanced breast cancer; US 1998: Risk reduction in high-risk women
- Dosing: Oral; 20 mg once daily for 5-10 years

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Tamoxifen
- FDA label (DailyMed): https://dailymed.nlm.nih.gov/dailymed/search.cfm?query=Tamoxifen

## Connected records

- cancers: [Ductal carcinoma in situ (DCIS)](https://onco.cc/cancers/ductal-carcinoma-in-situ/), [High-risk early HR-positive breast cancer](https://onco.cc/cancers/hr-positive-early-high-risk/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Inflammatory breast cancer](https://onco.cc/cancers/inflammatory-breast-cancer/), [Invasive cribriform carcinoma of the breast](https://onco.cc/cancers/invasive-cribriform-carcinoma-breast/), [Invasive lobular carcinoma of the breast](https://onco.cc/cancers/invasive-lobular-carcinoma/), [Lobular carcinoma in situ (LCIS)](https://onco.cc/cancers/lobular-carcinoma-in-situ/), [Male breast cancer](https://onco.cc/cancers/male-breast-cancer/), [Mucinous carcinoma of the breast](https://onco.cc/cancers/mucinous-carcinoma-breast/), [Paget disease of the nipple](https://onco.cc/cancers/paget-disease-of-the-nipple/), [Papillary carcinomas of the breast (encapsulated, solid and invasive papillary)](https://onco.cc/cancers/papillary-carcinoma-breast/), [Tubular carcinoma of the breast](https://onco.cc/cancers/tubular-carcinoma-breast/)
- technologies: [Acupuncture for hot flushes on endocrine therapy](https://onco.cc/technologies/acupuncture-hot-flushes/), [Antiandrogens for hair: spironolactone, finasteride, dutasteride](https://onco.cc/technologies/hair-antiandrogens-alopecia/), [Bone loss caused by cancer treatment, and what rebuilds it](https://onco.cc/technologies/cancer-treatment-bone-loss/), [Chemoprevention & risk-reducing surgery](https://onco.cc/technologies/chemoprevention/), [Dietitian-led weight-loss programmes in HR-positive breast cancer](https://onco.cc/technologies/dietitian-led-weight-loss-breast/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/), [FES PET (oestrogen receptor imaging)](https://onco.cc/technologies/fes-pet/), [Menopause brought on by cancer treatment, and the options for it](https://onco.cc/technologies/menopause-after-cancer-treatment/), [Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss](https://onco.cc/technologies/minoxidil-chemotherapy-alopecia/), [Ovarian function after chemotherapy: who recovers, and when](https://onco.cc/technologies/ovarian-function-after-chemotherapy/), [Soy foods and breast cancer](https://onco.cc/technologies/soy-breast-cancer/), [Vaginal oestrogen after breast cancer: what the evidence says, and where it disagrees](https://onco.cc/technologies/vaginal-oestrogen-after-breast-cancer/)
- targets: [Estrogen receptor (ERα)](https://onco.cc/targets/estrogen-receptor/)
- companies: [AstraZeneca](https://onco.cc/companies/astrazeneca/)
- trials: [A Study of Abemaciclib (LY2835219) Plus Tamoxifen or Abemaciclib Alone in Women With Metastatic Breast Cancer](https://onco.cc/trials/nct02747004/), [A Study of Camizestrant in ER+/HER2- Early Breast Cancer After at Least 2 Years of Standard Adjuvant Endocrine Therapy](https://onco.cc/trials/nct05774951/), [A Study of Elacestrant Versus Standard Endocrine Therapy in Women and Men With ER+,HER2-, Early Breast Cancer With High Risk of Recurrence](https://onco.cc/trials/nct06492616/), [A Study of Imlunestrant (LY3484356) in Premenopausal Women With Estrogen Receptor-Positive (ER+) Human Epidermal Growth Factor Receptor 2 Negative (HER2-) Early Breast Cancer](https://onco.cc/trials/nct07287098/), [A Study of Imlunestrant Versus Standard Endocrine Therapy in Participants With Early Breast Cancer](https://onco.cc/trials/nct05514054/), [A Study of MK-5684 in People With Certain Solid Tumors (MK-5684-015/OMAHA-015)](https://onco.cc/trials/nct06979596/), [CALGB 9343](https://onco.cc/trials/calgb-9343/), [Combination Chemotherapy, Surgery, and Radiation Therapy With or Without Dexrazoxane and Trastuzumab in Treating Women With Stage III or Stage IV Breast Cancer](https://onco.cc/trials/nct00016276/), [COMET (Comparison of Operative versus Monitoring and Endocrine Therapy)](https://onco.cc/trials/comet-dcis/), [DBCG 82b and 82c](https://onco.cc/trials/dbcg-82bc/), [Efficacy of Tamoxifen Versus Toremifene in CYP2D6 IM/PM of Premenopausal Patients With ER-positive Early Breast Cancer](https://onco.cc/trials/nct03351062/), [First-in-Human Study of Tersolisib (STX-478) as Monotherapy and in Combination With Other Antineoplastic Agents in Participants With Advanced Solid Tumors](https://onco.cc/trials/nct05768139/), [HOBOE: A Phase 3 Study of Adjuvant Triptorelin and Tamoxifen, Letrozole, or Letrozole and Zoledronic Acid in Premenopausal Patients With Breast Cancer](https://onco.cc/trials/nct00412022/), [IBIS-I (International Breast Intervention Study I)](https://onco.cc/trials/ibis-i/), [IBIS-II (International Breast Intervention Study II)](https://onco.cc/trials/ibis-ii/), [Investigating the Potential Role of a Novel Quadrate Combination Therapy Mifepristone(Antiprogestrone), Tamoxifen, Retinoic Acid and Cannabidiol ( Selective Cyp 26 Inhibitor) for Treating Early Breast Cancer](https://onco.cc/trials/nct05016349/), [Ovarian Suppression Evaluating Subcutaneous Leuprolide Acetate in Breast Cancer](https://onco.cc/trials/nct04906395/), [SOFT & TEXT](https://onco.cc/trials/soft-text/), [TAM-01](https://onco.cc/trials/tam-01/), [Tamoxifen and Pegylated Liposomal Doxorubicin for the Treatment of Patients With Metastatic or Inoperable, Locally Advanced Triple Negative Breast Cancer](https://onco.cc/trials/nct06434064/), [Triptorelin With Either Exemestane or Tamoxifen in Treating Premenopausal Women With Hormone-Responsive Breast Cancer](https://onco.cc/trials/nct00066703/)
- terms: [Aromatase inhibitor](https://onco.cc/terms/aromatase-inhibitor/), [Chemoprevention (tamoxifen, anastrozole, raloxifene) and ER-negative breast cancer](https://onco.cc/terms/chemoprevention-and-er-negative-breast-cancer/), [Choices made at the time of treatment that change the second cancer risk](https://onco.cc/terms/rejuv-second-choices-made-at-treatment/), [Ductal carcinoma in situ (DCIS)](https://onco.cc/terms/dcis/), [Endocrine-therapy-induced alopecia](https://onco.cc/terms/alopecia-endocrine-therapy/), [Ovarian function suppression (OFS)](https://onco.cc/terms/ovarian-function-suppression/), [Selective oestrogen receptor degrader (SERD)](https://onco.cc/terms/serd/), [Venous thromboembolism (VTE)](https://onco.cc/terms/vte/)
- people: [Bernard Fisher](https://onco.cc/people/bernard-fisher/)
- ideas: [Pool purchasing of essential cancer medicines across countries](https://onco.cc/ideas/idea-cost-pooled-procurement-essential/), [Transparent cost-plus pricing for every oral oncology generic](https://onco.cc/ideas/idea-cost-transparent-generic-pricing/)
- key papers: [IBIS-I: five years of tamoxifen keeps preventing breast cancer for at least 20 years](https://onco.cc/key-papers/paper-ibis-i-tamoxifen-lancet-oncol-2015/)
- institutions: [UPMC Hillman Cancer Center](https://onco.cc/institutions/upmc-hillman/)
- drugs: [Anastrozole](https://onco.cc/drugs/anastrozole/), [Raloxifene](https://onco.cc/drugs/raloxifene/), [Toremifene](https://onco.cc/drugs/toremifene/)
- biomarkers: [ER status (oestrogen receptor by IHC)](https://onco.cc/biomarkers/er-status/), [PR status (progesterone receptor by IHC)](https://onco.cc/biomarkers/pr-status/)
- roadmaps: [Cancer prevention roadmap: tobacco control and vaccines → biomarker-guided chemoprevention → interception in carriers](https://onco.cc/roadmaps/prevention-roadmap/), [Hormonal therapy roadmap: removing the ovaries → tamoxifen → oral degraders switched by a blood test](https://onco.cc/roadmaps/hormonal-therapy-roadmap/), [Targeted therapy roadmap: imatinib → designed for resistance → the undruggable drivers fall](https://onco.cc/roadmaps/targeted-therapy-roadmap/)
- pathways: [Breast cancer (KEGG map)](https://onco.cc/pathways/breast-cancer-signalling/), [Chemical carcinogenesis - receptor activation](https://onco.cc/pathways/chemical-carcinogenesis-receptor-activation/)

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JSON: https://onco.cc/api/v1/entities/tamoxifen.json