In women, particularly those with a personal or strong family history of breast cancer, does spironolactone increase the risk of developing breast cancer?

Spironolactone Does Not Increase Breast Cancer Risk

Based on the strongest available evidence, spironolactone does not increase the risk of breast cancer in women, including those with a personal or strong family history of breast cancer. 1

Evidence from Large-Scale Studies

The most recent and comprehensive guideline evidence comes from the 2024 American Academy of Dermatology Guidelines of Care, which references a systematic review of 7 studies encompassing 4.5 million individuals. This analysis found no statistically significant association between spironolactone use and breast cancer risk (RR 1.04; 95% CI 0.86-1.22) 1. This finding is based on low to very low certainty of evidence, but the consistency across multiple large studies is reassuring.

Earlier guideline evidence from 2016 further supports this conclusion, citing:

• A large retrospective matched cohort study of 1.29 million women (≥55 years) with 8.4 million patient-years of use found no association between spironolactone and breast cancer 2
• Another large retrospective cohort study of 2.3 million women representing 28.8 million person-years showed no association with breast, uterine, cervical, or ovarian cancers 2

Understanding the Black Box Warning

The FDA black box warning on spironolactone regarding tumorigenicity stems from animal studies using up to 150 times human doses, which showed development of various tumors including breast adenomas 2, 3. However, this animal data has not translated to human risk.

Only one human case report has suggested carcinogenicity, identifying 5 hospitalized patients with breast cancer taking spironolactone among other medications, but subsequent longitudinal and retrospective studies found no association 2.

Clinical Application for High-Risk Women

For women with a personal or strong family history of breast cancer, the 2019 guideline specifically addresses this concern: "In our practice, for patients with a family history of breast or ovarian cancer, we will still consider its use after a thorough discussion of the black box warning" 4. This reflects expert consensus that the theoretical concern does not outweigh clinical utility when properly discussed.

Additional research evidence supports safety even in breast cancer survivors:

• A 2020 retrospective analysis found no independent association between spironolactone and increased breast cancer recurrence (adjusted HR 0.966; 95% CI 0.807-1.156) 5
• A 2019 study of breast cancer patients receiving endocrine therapies found no evidence of interactions or increased risk with spironolactone use 6

Practical Recommendations

You can prescribe spironolactone to women with family history of breast cancer after informed discussion. The conversation should acknowledge:

1. The FDA black box warning exists based on high-dose animal studies
2. Multiple large human studies totaling over 30 million person-years show no increased risk
3. The most recent systematic review (2024) confirms no association with breast cancer

For women with personal history of breast cancer:

• Spironolactone appears safe and does not increase recurrence risk 5
• No drug interactions with endocrine therapies (tamoxifen, aromatase inhibitors) have been documented 6
• Consider individual discussion with the patient's oncologist if there are concerns

Common Pitfall to Avoid

Do not withhold spironolactone solely based on family history of breast cancer. The evidence overwhelmingly demonstrates safety, and the black box warning reflects animal toxicology data that has not manifested in human populations despite extensive real-world use.