Ovarian carcinoma arising in atypical endometriosis.

Malignant transformation is a rare but recognized complication of gonadal and extragonadal endometriosis. Morphologic documentation of the continuous transition from benign endometrioid epithelium through epithelial atypia to invasive carcinoma within the same organ is necessary to prove that the cancer arose from endometriosis. This stringent criterion, put forward by Scott, has rarely been fulfilled. We report a case with a chronologic association between ovarian endometriosis showing foci of atypia and a subsequent large clear-cell carcinoma arising in the same ovary 3 years later. We recommend close scrutiny of cellular atypia in endometriosis to define lesions that may be preneoplastic and require an extended surgical approach.