Tamoxifen
| Evidence Level: L4 | Predicted Indications: 10 |
Table of Contents
Tamoxifen: From Breast Cancer to Mammary Paget Disease
One-Sentence Summary
Tamoxifen is an oral hormone therapy used for estrogen receptor (ER)-positive breast cancer. The label text was not included in the Evidence Pack, so the original indication is inferred from the pack’s rationale notes. The TxGNN model predicts it may help in mammary Paget disease, but the supporting evidence is thin: 1 clinical trial, which does not test efficacy, and 13 publications, mostly case reports and case series.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | ER-positive breast cancer (inferred; US license indication text is blank in the pack) |
| Predicted New Indication | Mammary Paget disease |
| TxGNN Prediction Score | 99.69% |
| Evidence Level | L4 |
| US Market Status | ✓ Marketed |
| Number of NDAs | 17 (the five listed are all ANDAs) |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available. Based on known information, tamoxifen is an endocrine (anti-estrogen) therapy whose efficacy in hormone receptor-positive breast cancer is well established. It may be mechanistically applicable to mammary Paget disease.
Mammary Paget disease usually occurs together with an underlying ductal carcinoma in situ (DCIS) or invasive carcinoma. Tamoxifen would therefore most plausibly act as adjuvant endocrine therapy for a hormone receptor-positive underlying tumor. It would not be a treatment specific to Paget disease.
The evidence is limited to case reports and small series. One case report shows a response in metastatic extramammary Paget disease, but that finding does not transfer to the mammary form.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrollment | Key Findings |
|---|---|---|---|---|
| NCT00002920 | Phase 3 | Completed | 313 | Tests medroxyprogesterone acetate versus observation to prevent endometrial disorders in postmenopausal women taking tamoxifen. Eligible patients include those with Paget’s disease of the nipple. This addresses a tamoxifen side effect, not its efficacy in Paget disease. |
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 25759627 | 2014 | Meta-analysis | Breast Care | Local recurrence after mastectomy versus breast-conserving surgery for Paget’s disease. Recurrence is as high as 20–40% in the literature. It is not about tamoxifen. |
| 34463889 | 2022 | Case report | Investigational New Drugs | Successful tamoxifen treatment of hormone receptor-positive metastatic extramammary Paget disease. |
| 14965622 | 2001 | Case report | Breast | Unusually extensive Paget’s disease of the nipple. The patient responded to tamoxifen and was also treated with radiotherapy. |
| 1648987 | 1991 | Case series | Br J Surg | 48 women with nipple Paget’s disease. Most were treated with mastectomy or cone excision, and only one received tamoxifen. |
| 16277886 | 2005 | Cohort | Clin Breast Cancer | Paget’s disease of the nipple as a local recurrence after breast-conservation treatment (2,181 patients). |
| 29694313 | 2018 | Case report | Il Giornale di Chirurgia | Paget disease of the male breast. There are no standard guidelines, and it can hide an invasive ductal cancer. |
| 8955252 | 1996 | Case report and review | Am Surg | Male breast Paget’s disease: one case plus a review of 32 published cases. |
| 12924421 | 2003 | Case report | Surgery Today | Synchronous bilateral breast cancer with Paget’s disease and invasive ductal carcinoma. |
| 19112575 | 2009 | Case report | Arch Gynecol Obstet | Vulvar and breast Paget’s disease with synchronous underlying cancer. |
| 17319355 | 2006 | Case series | Niger J Clin Pract | 8 of 240 breast cancer patients (3.3%) in Benin City had nipple Paget’s disease. |
No randomized controlled trials were found for this indication.
US Market Information
The pack lists 17 authorizations. The five below are the main ones. The approved-indication text is blank for all of them in the pack, so that column is omitted.
| Authorization Number | Product Name | Dosage Form | Manufacturer |
|---|---|---|---|
| ANDA070929 | Tamoxifen Citrate | Tablet | Bryant Ranch Prepack |
| ANDA074732 | Tamoxifen Citrate | Tablet | Mylan Pharmaceuticals Inc. |
| ANDA213358 | Tamoxifen Citrate | Tablet, film coated | Aurobindo Pharma Limited |
| ANDA213358 | Tamoxifen Citrate | Tablet, film coated | Bryant Ranch Prepack |
| ANDA070929 | Tamoxifen Citrate | Tablet | A-S Medication Solutions |
Cytotoxicity
The pack has no toxicity data. The entries below come from general drug-class knowledge and should be checked against the package insert.
| Item | Content |
|---|---|
| Cytotoxicity Classification | Hormonal (endocrine) therapy, selective estrogen receptor modulator (SERM). Not a conventional cytotoxic. |
| Myelosuppression Risk | Low |
| Emetogenicity Classification | Low |
| Monitoring Items | CBC, liver function, signs of thromboembolism, endometrial symptoms (abnormal vaginal bleeding) |
| Handling Protection | Follow institutional hazardous drug handling policy. Please refer to the package insert warnings and precautions. |
Safety Considerations
Please refer to the package insert for safety information.
Conclusion and Next Steps
Decision: Hold
Rationale: The high TxGNN score is not backed by clinical evidence for mammary Paget disease. The only trial concerns a tamoxifen side effect, and the literature is case reports and surgical series. Tamoxifen’s most plausible role is as endocrine therapy for the underlying hormone receptor-positive tumor, which is not novel repurposing.
To proceed, the following is needed:
- The FDA package insert (warnings and contraindications). This is a blocking gap that prevents safety screening.
- Mechanism of action data from DrugBank.
- Prospective or well-designed retrospective data on tamoxifen in mammary Paget disease with hormone receptor testing of the underlying tumor.
- A route-compatibility check, which is still pending.
Note on other predictions: Two other predictions for this drug have much stronger evidence. Breast carcinoma in situ is rated L1 and supported by Phase 3 RCTs and a Cochrane meta-analysis. ER-positive breast cancer is also rated L1. Both appear to be established uses rather than novel repurposing signals, and both are rated “Proceed with Guardrails” in the pack.
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.