PCOS and breast cancer: 18 studies reviewed, association modest and still unsettled
Summary
A systematic review in the European Journal of Obstetrics, Gynecology and Reproductive Biology (20 June 2026) brought together 18 studies — observational cohorts, Mendelian randomisation analyses and bioinformatic work — on whether PCOS/PMOS changes breast cancer risk. The authors describe a possible modest association, somewhat more visible in premenopausal women and in those with hyperandrogenic features. They are explicit that the body of evidence remains heterogeneous and inconclusive: study designs, how PCOS was defined, and how long women were followed all differ widely, and the Mendelian randomisation results do not line up neatly with the observational ones. No single risk figure can responsibly be quoted from this review, which is itself the finding worth reporting.
Why it matters for you
This is a 'do not panic, do not ignore' result. It is not a reason to change screening on your own — in most countries PCOS alone does not move you into a high-risk screening programme. It is a reason to keep up the standard screening for your age and country, and to mention PCOS when a clinician reviews your overall risk alongside family history and other factors.