Is polycystic ovary syndrome, a state of relative estrogen excess, a real risk factor for estrogen-dependant malignancies?

Polycystic ovary syndrome (PCOS) is a common endocrinopathy affecting women of fertile age. It is associated with several risk factors and long-term health consequences. Chronic anovulation combined with relative estrogen excess and consequent prolonged stimulatory effect on the endometrium can lead to the pathogenesis of hormonal dependant carcinoma. PCOS is thus traditionally reported to be associated with increased risk of endometrial, as well as breast and ovarian cancers. This article provides a critical literature review of the relationship between PCOS and the incidence of estrogen-dependant gynecological tumours, and it then discusses whether the commonly cited risk factor association can be substantiated by high quality studies which comply with the requirements of "evidence-based medicine."