Does using spironolactone increase the risk of breast cancer?

Question

I have been prescribed spironolactone for female pattern hair loss but have heard confusing information about whether or not the drug increases the risk of breast cancer. Do women using spironolactone have an increased risk of breast cancer?

Answer

Thanks for the great question. I’ll answer this with some depth but I’ll begin by saying that the most recent well conducted studies do not support an association between breast cancer and the use of spironolactone in women at low risk for the disease.

Concerns about the possibility of an increased risk of cancer from spironolactone date back to 1975. Studies at the time showed that rats ingesting spironolactone (at 25–250 times the exposure dose in humans) for 2 years developed several types of tumors including benign adenomas of the thyroid and testes, malignant mammary tumors, and growths on the liver.

To date, there is no good evidence to support the notion that women using spironolactone are at increased risk for breast cancer. In the most recent 2017 study, McKenzie studied the risk of cancer among users of Spironolactone. The participants were 74 272 patients exposed to spironolactone between 1986 and 2013 using the Clinical Practice Research Datalink from the UK. In this study, there was no increased risk of cancer in spironolactone users. 

In 2013, Biggar published data specifically looking at the risk of breast cancer in female spironolactone users. The researchers used anationwide prescription drug registry between 1995 and 2010 and identified use of spironolactone in a cohort of Danish women (≥20 years old).  After studying 2.3 million women (28.5 million person-years), the authors concluded that with respect to breast, uterus, ovarian and cervical cancer, there is no evidence of increased risk with spironolactone or furosemide use.

In 2012, McKenzie published a study a retrospective cohort study evaluating whether exposure to spironolactone treatment affects the risk of incident breast cancer in women over 55 years of age. The study involved 1,290,625 female patients, older than 55 years and with no history of breast cancer, from 557 general practices with a total follow-up time of 8.4 million patient years.  Although the vast majority of women were using doses under 100 mg, 17.2 % of women in the study were using 100 mg doses and 3.6 % were using 200 mg doses. The data suggested that the use of spironolactone did not increase the risk of breast cancer.

Summary and Conclusion

The evidence to date does not point to an association between spironolactone and breast cancer in women at low risk. These studies above were conducted in women with low risk of breast cancer and not in women at highest risk and not in women who already have breast cancer. This is important to keep in mind. Many physicians continue to avoid avoid prescribing spironolactone to patients with a history of breast cancer (or at highest risk of breast cancer) given that no such studies have been done. However, for most women, there is no evidence to suggest that their use of spironolactone increases their risk of developing breast cancer.

References

Barker DJP. The epidemiological evidence relating to spironolactone and malignant disease in man. J Drug Dev. 1978;1(Suppl 1. 2):22–25.

Biggar RJ, et al. Spironolactone use and the risk of breast and gynecologic cancers.Cancer

Epidemiol. 2013.

Danielson DAN, Jick H, Hunter JR, et al. Nonestrogenic drugs and breast cancer. Am J Epidemiol. 1982;116:329–332. 

Mackenzie IS, et al. Spironolactone use and risk of incident cancers: a retrospective, matched

cohort study. Br J Clin Pharmacol. 2017.

Mackenzie IS, et al. Spironolactone and risk of incident breast cancer in women older than 55

years: retrospective, matched cohort study. BMJ. 2012.