Tamoxifen
| Evidence Level: L4 | Predicted Indications: 10 |
Table of Contents
Tamoxifen: From Breast Carcinoma to Mammary Paget Disease
One-Sentence Summary
Tamoxifen is an estrogen receptor-blocking drug originally used to treat breast carcinoma (female breast carcinoma, invasive ductal carcinoma and ductal adenocarcinoma). The TxGNN model predicts it may be effective for Mammary Paget Disease, but the only listed trial (1 clinical trial) tests a different drug for a tamoxifen side effect, and the 10 publications are mostly case reports, case series and recurrence studies. Evidence for this specific prediction is therefore weak (model prediction plus case-level reports).
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Female breast carcinoma (the approved indication text is not available in the Singapore licence records; this is taken from the knowledge-graph indication list) |
| Predicted New Indication | Mammary Paget disease |
| TxGNN Prediction Score | 99.69% |
| Evidence Level | L4 |
| Singapore Market Status | ✓ Marketed |
| Number of Registrations | 4 |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available. Based on known information, tamoxifen is a selective estrogen receptor modulator (SERM) that blocks estrogen signalling in breast tissue. Its efficacy in hormone receptor-positive breast cancer is well established.
Mammary Paget disease is usually associated with underlying ductal carcinoma in situ or invasive breast cancer, which is often hormone receptor-positive. Estrogen receptor blockade is therefore plausible. However, this is an extension of tamoxifen's existing breast cancer use, not independent repurposing evidence. Case reports suggest responses (a case of extramammary Paget disease and an extensive nipple Paget case), but these are isolated observations.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrollment | Key Findings |
|---|---|---|---|---|
| NCT00002920 | Phase 3 | Completed | 313 | Medroxyprogesterone acetate vs observation to prevent endometrial disease in postmenopausal breast cancer patients (including Paget's disease of the nipple) taking tamoxifen. It addresses a tamoxifen side effect, not efficacy against Paget disease. |
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 34463889 | 2022 | Case report | Investigational New Drugs | Successful tamoxifen treatment of hormone receptor-positive metastatic extramammary Paget disease |
| 14965622 | 2001 | Case report | Breast | Extensive nipple Paget disease; a response was achieved with tamoxifen, together with radiotherapy |
| 25759627 | 2014 | Cohort (meta-analysis) | Breast Care | Local recurrence after mastectomy vs breast-conserving surgery for Paget's disease (recurrence 20-40%) |
| 1648987 | 1991 | Review | British Journal of Surgery | 48 women with nipple Paget's disease; mostly surgical treatment, tamoxifen used in one case |
| 16277886 | 2005 | Cohort | Clinical Breast Cancer | Paget's disease of the nipple as local recurrence after breast-conserving treatment |
| 17319355 | 2006 | Case series | Nigerian Journal of Clinical Practice | Paget's disease of the nipple-areola complex in 8 of 240 breast cancer patients |
| 8955252 | 1996 | Case report | American Surgeon | Paget's disease of the male breast with a review of 32 cases |
| 19112575 | 2009 | Cohort | Archives of Gynecology and Obstetrics | Vulvar and breast Paget's disease with synchronous underlying cancer |
| 12924421 | 2003 | Case report | Surgery Today | Synchronous bilateral breast cancer with Paget's disease and invasive ductal carcinoma |
| 18288984 | 2008 | Review | Current Medicinal Chemistry | Therapies for bone loss, including estrogen receptor modulators; only indirectly relevant |
Singapore Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| SIN06409P | NOVOFEN 20 TABLET 20 mg | Tablet | Not available in the compiled data |
| SIN07094P | TAMOXIFEN TABLET 20 mg | Film-coated tablet | Not available in the compiled data |
| SIN00796P | NOLVADEX-D TABLET 20 mg | Film-coated tablet | Not available in the compiled data |
| SIN00794P | NOLVADEX TABLET 10 mg | Film-coated tablet | Not available in the compiled data |
Cytotoxicity
| Item | Content |
|---|---|
| Cytotoxicity Classification | Targeted/endocrine therapy (selective estrogen receptor modulator), not a conventional cytotoxic |
| Myelosuppression Risk | Low in general; the knowledge graph lists leukopenia and thrombocytopenia as contraindication-related conditions, so blood counts should be monitored |
| Emetogenicity Classification | Low |
| Monitoring Items | Please refer to the package insert warnings and precautions (suggested: CBC, liver function, calcium, gynaecological assessment) |
| Handling Protection | Please refer to the package insert warnings and precautions |
Safety Considerations
- Conditions flagged as contraindications in the knowledge graph (not label text): thrombocytopenia, leukopenia, hypercalcemia, nephrocalcinosis, phosphorus metabolism disease, stroke and cerebrovascular disorders, cerebral infarction, pulmonary embolism, vision disorder and blindness.
- Drug interactions: 100 interactions were found. Major interactions among those listed include bupropion, lorcaserin, cimetidine, dolasetron, eliglustat, cisapride, dexfenfluramine and fenfluramine. Moderate ones include famotidine, loperamide, aprepitant, dexamethasone, clarithromycin, granisetron and levofloxacin.
- Related risks from the supporting data: venous thromboembolism and endometrial cancer (relevant to long-term use, per the DCIS and ER-positive evidence).
Please refer to the package insert for full warnings and contraindications.
Conclusion and Next Steps
Decision: Hold
Rationale: The prediction is biologically plausible because Paget disease of the breast is usually accompanied by underlying breast carcinoma, but there is no trial testing tamoxifen in this condition. Evidence is limited to case reports and observational studies, and this is an extension of an existing breast cancer indication rather than independent confirmation.
To proceed, the following is needed:
- Hormone receptor status data for Paget disease cohorts, and prospective or comparative studies of tamoxifen
- Singapore package insert warnings and contraindications (not yet obtained)
- Mechanism of action data
- Approved indication text for the four Singapore licences
Other predicted indications of note (from the same analysis):
- Breast carcinoma in situ (DCIS): Evidence L1, Proceed with Guardrails. Placebo-controlled low-dose tamoxifen trial TAM-01 (PMIDs 30973790 and 36917758) and the Cochrane review support its use in ER-positive disease. This is largely an established use, not novel repurposing.
- Estrogen-receptor positive breast cancer: Evidence L1, Proceed with Guardrails. This is the original approved use.
- Hormone-resistant breast carcinoma: Research question only, as tamoxifen alone is unlikely to help.
- Invasive tubular breast carcinoma: Hold, with indirect evidence only.
- Basal-like breast carcinoma, Ehrlich tumor carcinoma, intraductal cribriform breast adenocarcinoma, sebaceous breast carcinoma and botryoid-type embryonal rhabdomyosarcoma of the vagina: Hold, with no clinical support or an unfavourable mechanism.
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.