ARID1A expression in ovarian clear cell carcinoma with an adenofibromatous component

Aims: The carcinogenesis of ovarian clear cell carcinoma (CCC) has been hypothesized to comprise two different pathways: an adenofibroma-carcinoma sequence and an endometriosis-carcinoma sequence. However, the difference in the genetic basis of these two pathways remains unclear. Recent studies have suggested that an ARID1A mutation and the loss of the corresponding protein, BAF250a, are frequent events in CCC. Herein, we investigated the difference in the loss of BAF250a expression in adenofibroma-related CCC and endometriosis-related CCC. Methods and results: In total, 93 cases of surgically treated CCC were evaluated. The presence of adenofibroma and endometriosis associated with carcinoma was determined by reviewing haematoxylin and eosin-stained slides for each case. BAF250a expression in carcinoma was examined immunohistochemically. The loss of BAF250a expression was detected in carcinomas in 50 of 93 (54%) cases, including five of 18 (28%) with adenofibroma alone, 30 of 45 (67%) with endometriosis alone, eight of 18 (44%) with both conditions and seven of 12 (58%) with neither condition. The loss of BAF250a expression was significantly less frequent in CCC cases with adenofibroma than in cases with endometriosis (P = 0.01, Fisher's exact test). Conclusions: The action of ARID1A in carcinogenesis differs between adenofibroma-related CCC and endometriosis-related CCC.