In a study that included 23 clear cell carcinomas with synchronous putative precursor lesions (i.e., endometriosis adjacent to carcinoma, with or without cytological atypia), as many as 43% (10/23) of ovarian clear cell carcinomas and 90% (9/10) of the coexisting endometriotic epithelium adjacent to the clear cell carcinoma presented PIK3CA gene mutations [124]. Here, PIK3CA is linked to endometriosis.