Polycystic ovary syndrome and breast cancer risk: a systematic review

Polycystic ovary syndrome (PCOS), now termed polyendocrine metabolic ovarian syndrome (PMOS), is a common endocrine disorder characterized by hormonal and metabolic alterations that may influence cancer risk. While the association with endometrial cancer is well established, evidence regarding breast cancer risk remains inconsistent. This systematic review aimed to evaluate and synthesize current evidence on the association between PMOS/PCOS and breast cancer risk.

A systematic search of PubMed/MEDLINE, the Cochrane Library, and Web of Science was conducted up to October 2025 following PRISMA 2020 guidelines. Observational studies, Mendelian randomization studies, and bioinformatic analyses assessing breast cancer risk in women with PMOS/PCOS were included. Study quality was assessed using validated tools appropriate to study design.

Eighteen studies met the inclusion criteria, comprising case-control and cohort studies, as well as genetic and bioinformatic analyses. Results were heterogeneous. Several large cohort studies and genetic analyses suggested a modest increase in breast cancer risk, particularly among premenopausal women and those with hyperandrogenic features, whereas other studies reported no association or a reduced risk. Variability in diagnostic criteria, study design, confounder adjustment, and population characteristics likely contributed to these inconsistencies.

Current evidence indicates a possible modest association between PMOS/PCOS and breast cancer risk, although findings remain inconclusive. Any absolute increase in risk appears limited and does not justify changes to current screening practices. Further research using standardized diagnostic criteria and improved stratification by phenotype, age, and menopausal status is warranted.