From the Guidelines
Finasteride should be avoided in patients with a history of breast cancer due to its potential impact on hormone-sensitive cancer recurrence risk. This decision is based on the principle of prioritizing morbidity, mortality, and quality of life, and considering the hormonal effects of finasteride, which inhibits the conversion of testosterone to dihydrotestosterone (DHT) by blocking the 5-alpha-reductase enzyme 1. The management of male breast cancer, as outlined in the ASCO guideline published in the Journal of Clinical Oncology in 2020, emphasizes the importance of endocrine therapy and careful consideration of hormonal treatments in patients with a history of breast cancer 1.
Given the potential for finasteride to alter the balance of androgens and estrogens in the body, it is prudent to consider alternative treatments that do not affect hormone pathways for conditions such as hair loss or benign prostatic hyperplasia. If finasteride is deemed absolutely necessary, consultation with the patient's oncologist is crucial to weigh the potential risks against benefits, taking into account the specific type of breast cancer, time since diagnosis, current cancer status, and other treatment options available. Key factors to consider include the patient's history of hormone receptor–positive breast cancer and whether they have been treated with tamoxifen or other endocrine therapies, as these factors can influence the decision to use finasteride 1.
In practice, the approach to managing patients with a history of breast cancer involves careful consideration of their individual risk factors, cancer history, and current health status, as well as adherence to guidelines that prioritize evidence-based treatments and minimize potential risks, such as those associated with finasteride use 1.
From the FDA Drug Label
The MTOPS Study was not specifically designed to make statistical comparisons between groups for reported adverse experiences. Four patients in MTOPS reported the adverse experience breast cancer Three of these patients were on finasteride only and one was on combination therapy. During the 4- to 6-year placebo- and comparator-controlled MTOPS study that enrolled 3,047 men, there were 4 cases of breast cancer in men treated with finasteride but no cases in men not treated with finasteride During the 7-year placebo-controlled Prostate Cancer Prevention Trial (PCPT) that enrolled 18,882 men, there was 1 case of breast cancer in men treated with finasteride, and 1 case of breast cancer in men treated with placebo. The relationship between long-term use of finasteride and male breast neoplasia is currently unknown
- male breast cancer
Finasteride and Breast Cancer: The FDA drug label reports cases of breast cancer in men treated with finasteride.
- Key Points:
- Four cases of breast cancer were reported in the MTOPS study, with three cases in men treated with finasteride only and one case in a man treated with combination therapy.
- The relationship between long-term use of finasteride and male breast neoplasia is currently unknown.
- Clinical Decision: Due to the uncertainty of the relationship between finasteride and breast cancer, caution should be exercised when prescribing finasteride to a patient with a history of breast cancer. It is essential to weigh the potential benefits of finasteride against the potential risks and consider alternative treatment options. 2
From the Research
Finasteride Prescription for Patients with a History of Breast Cancer
- There is limited research directly addressing the prescription of finasteride for patients with a history of breast cancer.
- A study from 2018 3 found an increased risk of male breast cancer among finasteride users, but the analysis suggested possible ascertainment bias and did not support a clear relationship between dispensed finasteride and male breast cancer.
- Another study from 2019 4 found that 5-alpha reductase inhibitors, including finasteride, increase the risk of gynecomastia and breast tenderness in men treated for benign prostatic hyperplasia, but the risk of breast cancer was not significantly increased.
- The available evidence does not provide clear guidance on the safety of prescribing finasteride for patients with a history of breast cancer, and further research is needed to confirm the results.
- Studies on the use of finasteride in patients with benign prostatic hyperplasia 5, 6 do not address the specific concern of breast cancer history.
- A study on hormone replacement therapy in women with a history of breast cancer 7 does not provide relevant information on the use of finasteride in this population.