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Antipsychotic Drug Use and Postmenopausal Breast Cancer Risk in the Women’s Health Initiative (WHI): A Prospective Cohort Study

Breast cancer is the most prevalent form of cancer and the second leading cause of mortality, affecting 1 in 9 women in the United States. Recent studies have shown that antipsychotic drug use is associated with increased prolactin levels, which, in turn, is associated with increased risk of breast cancer. However, studies of the association between antipsychotic drug use and the risk of breast cancer are sparse and have largely been conducted in homogenous populations. Therefore, we evaluated this relationship in postmenopausal women (N = 119 524) in a diverse population of the Women’s Health Initiative (WHI) cohort. Antipsychotic drug use was self-reported and in situ and invasive breast cancer cases were confirmed by medical records for the WHI clinical trial (CT) and the WHI observational study (OS), from 1993 through 2018. We used Cox proportional hazards regression to model breast cancer risk against antipsychotic drug use while adjusting for dietary and lifestyle factors. Overall, antipsychotic users made up 0.41% of this population. There was no overall association between antipsychotic drug use and postmenopausal breast cancer risk (HR = 1.01, 95% CI = 0.73 – 1.40). Among typical antipsychotic drug users, there was a suggested two-fold increased risk in developing in situ breast cancer (HR = 2.02, 95% CI = 0.84, 4.86). Thus, antipsychotic drug use does not appear to increase breast cancer risk overall, but the potential association between antipsychotics and in situ breast cancer merits further study.