Breast Cancer Risk in over 1.3 Million Women on Antipsychotic Therapy: Life-Saving Drugs or Hidden Trigger for Breast Cancer?

Introduction: Antipsychotic (AP) medications are widely prescribed beyond psychotic disorders, yet their long-term safety profile regarding breast cancer (BC) risk remains uncertain. Methods: We conducted a systematic review and meta-analysis of observational studies evaluating the association between AP exposure and incident BC. Eligible studies reported adjusted odds ratios (ORs) with 95% confidence intervals for any AP, prolactin-increasing antipsychotics (PIAPs), or prolactin-sparing antipsychotics (PSAPs). Study quality was assessed using the modified Newcastle-Ottawa Scale (mNOS), and certainty of evidence was graded with the GRADE framework. Random-effect models were used to pool effect estimates by exposure category, duration, and cumulative Defined Daily Dose (DDD). Results: Nine high-quality observational studies encompassing 108 effect estimates were included. Most studies achieved mNOS scores of 9, yet GRADE certainty ranged from very low to moderate, with the overall body of evidence graded as low certainty due primarily to residual confounding. Any AP exposure was associated with a modestly increased BC risk, particularly with long-term use: use for >5 years yielded pooled ORs around 1.5–1.6, while short-to-medium duration (1–5 years) showed smaller increases (pooled ORs in the range 1.2–1.3). For PIAPs, both longer duration (>5 years) and higher cumulative exposure (>1000–2000 DDDs) were consistently associated with ORs/HRs in the 1.3–1.6 range, suggesting a possible dose–response pattern. Histological analyses indicated stronger associations for ductal than lobular BC, and elevated risks were observed across age strata, including women aged