Characteristics of clear cell ovarian cancer arising from endometriosis: a two center cohort study

Objective Endometrioid and clear cell ovarian tumors have been referred to as "endometriosis associated ovarian cancers". However, very few studies have compared clinical and prognostic features of endometriosis- associated cancers or cancers not associated with endometriosis according to specific histotypes. We have investigated clinical and histological features of the largest published series of clear cell ovarian cancers arising in endometriosis using a retrospective database. Methods Seventy three patients with a primary diagnosis of either pure clear cell ovarian cancer and mixed endometrioid-clear cell ovarian cancer have been divided into two groups according to the detection of cancer strictly arising from ovarian endometriosis or not (n = 27 and n = 46, respectively). Clinical and pathological data have been compared. Results Patients with clear cell carcinomas arising from endometriosis tend to be significantly younger (51.4 ± 10.0 and 58.4 ± 11.2 years, p = 0.02). FIGO stage, laterality, prevalence of pure versus mixed histology, and presence of synchronous endometrial carcinoma were not significantly different between the two groups. Unilateral ovarian involvement was more frequent in cases arising in endometriosis (85% vs 63%, p = 0.04). Ascites was not found in any of the endometriosis-associated cancer cases vs 19.5% in patients without endometriosis. The presence of endometriosis did not affect 5-year overall survival rates. Conclusions Endometriosis per se does not appear to be associated with a lower stage tumor or to predict prognosis in ovarian clear cell cancers. Unilateral involvement and reduced presence of ascites may be linked to the cystic nature of endometriosis which frequently presents as monolateral and in which associated tumors are more likely to be longer confined to the ovary before spreading.