Somatic PTEN mutations have been observed in the endometrium of women with endometriosis as well as in endometriosis and endometriosis-associated ovarian cancers [109,110,112], indicating that the inactivation of the PTEN tumour suppressor gene is an early event in the development of ovarian endometrioid and clear-cell adenocarcinoma [113,114]. The gene discussed is PTEN; the disease is ovarian cancer.