Among the precursor lesions adjacent to the 23 ARID1A-deficient carcinomas, 86% of the non-atypical endometriosis (12 of 14) and 100% of the atypical endometriosis (14 of 14), benign (3 of 3), and borderline (6 of 6) clear-cell adenofibroma components were found to be ARID1A deficient.
Of the nine cases of complex atypical endometrial hyperplasia, all showed BAF250a expression; however, of 10 cases of atypical endometriosis (the putative precursor lesion for ovarian clear cell and endometrioid carcinoma), one case showed loss of staining for BAF250a in the atypical areas, with retention of staining in areas of non-atypical endometriosis.