Spironolactone use and the risk of breast and gynecologic cancers.

Spironolactone, an aldosterone-antagonist, is associated with gynecomastia. Digoxin, which can also cause gynecomastia, has been associated with increased incidence of breast and uterus cancers. We therefore postulated that spironolactone use might also increase these cancer risks. Using a nationwide prescription drug registry between 1995 and 2010, we identified use of spironolactone in a cohort of Danish women (≥20 years old). In users and non-users, incidence rate ratios adjusted by age group and calendar-year examined risk of breast and uterus cancers, both estrogen-sensitive, and ovary and cervix cancers, both relatively estrogen-insensitive. As an added control exposure, risk ratios in women who used another diuretic, furosemide, were examined by the same approach. Among 2.3 million women (28.5 million person-years), risks of breast, uterus, ovary, and cervix cancers were generally increased about 10-30% in both spironolactone and furosemide users. In the first year of drug exposure, incidences were increased, especially for ovary cancers. However, incidence increases in the first year of use were not specific for estrogen-sensitive cancers, occurred with both spironolactone and furosemide, and were driven by exposures immediately prior to diagnosis. For drug exposure ≥1 years before cancer diagnosis, incidences of these cancers were not significantly increased. We conclude that associations observed with first use in the year immediately before cancer diagnosis were driven by reverse causality, i.e., because of treatment for symptoms related to the incipient cancer. With respect to breast, uterus, ovarian and cervical cancer, there is no evidence of increased risk with spironolactone or furosemide use.