Summary
Tamoxifen Citrate has reached the approved stage (maximum clinical phase 4) for at least one indication, so its use in Breast Cancer would be drug repurposing rather than first-in-human development. This does not mean it is approved for Breast Cancer. ClinicalTrials.gov lists 8 registered trials linking Tamoxifen Citrate to Breast Cancer: 1 is active or not yet recruiting; 6 have completed; 1 is terminated, withdrawn, suspended or of unknown status. The most advanced is Phase 3 (NCT00032136). It plans or enrolled 4400 participants. Registration activity spans 2001 to 2016. The literature layer holds 8 publications for this pair: 2 Cochrane reviews, 1 randomised controlled trial publication and 5 clinical trial publications. Publication years run from 1994 to 2010. Because at least one synthesis-level source exists (systematic review, meta-analysis or Cochrane review), this pair has been assessed beyond single studies, although the synthesis may concern a different indication.
The RepurpOS disease-intelligence file for Breast Cancer ranks 1462 candidate therapeutics from Open Targets, ChEMBL, DGIdb and PubMed; only a minority carry direct clinical evidence, and this page covers one of those. Spontaneous remission context recorded for the condition: Spontaneous regression documented but rare (<0.5%); 5-year survival stage I: ~99%; stage IV: ~28% overall, improving with modern therapy.
Evidence table
| Evidence tier | A · Strong |
|---|---|
| Evidence score | 72.0 (trials 29.0, literature 23.0, tier 15, approved bonus 5.0) |
| Registered trials | 8 total: 0 recruiting, 1 active / not yet recruiting, 6 completed, 1 other |
| Linked publications | 8 (5 clinical trial publications, 2 Cochrane reviews, 1 randomised controlled trial publication) |
| Agent type | Drug (Small molecule) |
| Development stage (any indication) | Approved |
| Mechanism / class | Not recorded |
| Data sources | DGIdb |
| Linked via biomarker / target | BRCA1 |
How the evidence score is calculated
- Each registered trial scores by status (recruiting / active / enrolling 3, completed 2.5, not yet recruiting 2, unknown 1, terminated / withdrawn / suspended 0.5) plus a phase bonus (phase 3-4 +2, phase 2 +1, phase 1 +0.5). The trial component is capped at 30.
- Each literature item scores by design (Cochrane review 5, meta-analysis 4, systematic review 3, RCT 3, clinical trial publication 2, curated reference 1.5, other PubMed record 1). The literature component is capped at 30.
- The existing evidence tier adds 15 (A / Strong), 10 (B / Moderate), 5 (C / Preliminary) or 0 (D / Anecdotal).
- Agents approved for any indication (max clinical phase 4) add 5, because an approved agent has an established safety profile that lowers the barrier to repurposing trials.
- The score ranks what has been studied, not what works. It does not read effect sizes or directions of effect.
Registered clinical trials
| NCT ID | Title | Status | Phase | Enrolment |
|---|---|---|---|---|
| NCT00032136 | Exemestane Compared With Tamoxifen in Treating Postmenopausal Women With Breast Cancer 2001 | completed | Phase 3 | 4,400 |
| NCT01712893 | Simultaneous Versus Sequential Use of Adjuvant Chemotherapy and GnRHa in Treating ER+,Premenopausal Breast Cancer 2009 | completed | Phase 3 | 216 |
| NCT00107263 | Zoledronate in Preventing Bone Loss in Postmenopausal Women Who Are Receiving Letrozole for Stage I, Stage II, or Stage IIIA Breast Cancer 2005 | completed | Phase 3 | 558 |
| NCT00793377 | Neoadjuvant Doxorubicin/Cyclophosphamide Followed by Docetaxel (AC-Doc) Versus Dose-Dense Doxorubicin and Docetaxel (ADoc) in Breast Cancer | completed | Phase 3 | 913 |
| NCT02747004 | A Study of Abemaciclib (LY2835219) Plus Tamoxifen or Abemaciclib Alone in Women With Metastatic Breast Cancer 2016 | active, not recruiting | Phase 2 | 234 |
| NCT02188745 | ER Reactivation Therapy for Breast Cancer 2016 | completed | Phase 2 | 19 |
| NCT02936206 | Examination of Breast Cancer Cells of Pre-menopausal and Post-menopausal Women Before and After Exposure to Tamoxifen or Fulvestrant. 2016 | terminated | Phase 1 | 2 |
| NCT02517593 | Genetic Risk Estimation of Breast Cancer Prior to Preventive Medication Uptake 2016 | completed | PHASE1, PHASE2 | 151 |
Published literature
- Cochrane review Drug use evaluation of tamoxifen focusing on off-label use in a managed care population in IsraelKahan NR, Waitman DA, Blackman S et al. · Journal of managed care pharmacy : JMCP · 2010 · PMID 20518588
- Cochrane review Systematic review: comparative effectiveness of medications to reduce risk for primary breast cancerNelson HD, Fu R, Griffin JC et al. · Annals of internal medicine · 2009 · PMID 19920271
- Clinical trial publication [Late phase II study of TAT-59 (miproxifene phospate) in advanced or recurrent breast cancer patients (a double-blind comparative study with tamoxifen citrate)]Nomura Y, Nakajima M, Tominaga T et al. · Gan to kagaku ryoho. Cancer & chemotherapy · 1998 · PMID 9644320
- Clinical trial publication Long-term tamoxifen citrate use and potential ocular toxicityGorin MB, Day R, Costantino JP et al. · American journal of ophthalmology · 1998 · PMID 9559735
- Clinical trial publication Effect of tamoxifen on measurements of hemostasis in healthy womenMannucci PM, Bettega D, Chantarangkul V et al. · Archives of internal medicine · 1996 · PMID 8790074
- Clinical trial publication Effect of tamoxifen on lumbar spine bone mineral density in postmenopausal women after 5 yearsLove RR, Barden HS, Mazess RB et al. · Archives of internal medicine · 1994 · PMID 7979855
- Clinical trial publication Bioequivalence of 20-mg once-daily tamoxifen relative to 10-mg twice-daily tamoxifen regimens for breast cancerBuzdar AU, Hortobagyi GN, Frye D et al. · Journal of clinical oncology : official journal of the American Society of Clinical Oncology · 1994 · PMID 8270984
- Randomized controlled trial Protein S and protein C level changes with adjuvant tamoxifen therapy in postmenopausal womenMamby CC, Love RR, Feyzi JM · Breast cancer research and treatment · 1994 · PMID 7981450
Mechanism and notes
No mechanism of action is recorded for this pair in the source databases.
OSMF's existing evidence tier for this pair is A (Strong), derived from the strength of the disease association recorded in DGIdb, in this case via the biomarker or target BRCA1. The tier describes how well the drug-disease link is documented, not how well the drug works.
Frequently asked questions
Is Tamoxifen Citrate approved for Breast Cancer?
Tamoxifen Citrate has reached the approved stage (maximum clinical phase 4) for at least one indication, so its use in Breast Cancer would be drug repurposing rather than first-in-human development. This does not mean it is approved for Breast Cancer. Approval status for the specific indication should always be confirmed with the relevant regulator and prescribing information.
Is Tamoxifen Citrate in clinical trials for Breast Cancer?
ClinicalTrials.gov lists 8 registered trials linking Tamoxifen Citrate to Breast Cancer: 1 is active or not yet recruiting; 6 have completed; 1 is terminated, withdrawn, suspended or of unknown status. The most advanced is Phase 3 (NCT00032136). It plans or enrolled 4400 participants. Registration activity spans 2001 to 2016.
What does the evidence show for Tamoxifen Citrate in Breast Cancer?
Tamoxifen Citrate has both completed registered trials and synthesis-level publications linked to Breast Cancer. That is the strongest profile in this database, but the summaries here do not extract effect sizes, so read the linked reviews for direction and magnitude of benefit. OSMF's existing evidence tier for this pair is A (Strong), derived from the strength of the disease association recorded in DGIdb, in this case via the biomarker or target BRCA1. The tier describes how well the drug-disease link is documented, not how well the drug works.
Cite this page
Data: ClinicalTrials.gov, PubMed, Open Targets, ChEMBL, DGIdb and the OSMF therapeutic agent database. Last updated 2026-07-05. Page built 2026-10-07.