ABSTRACT: Ovarian endometriosis has been associated with increased risk for ovarian clear cell carcinoma (CCC). Atypical endometriosis shares common molecular alterations with CCC and therefore, has been proposed as a precursor lesion of CCC, although it is unclear if benign endometriosis is pre-neoplastic. In this study, we examined some molecular alterations in ovarian benign endometriosis, atypical endometriosis, and CCC in comparison to papillary serous carcinoma (PSC). These included BAF250a (encoded by ARID1A), a recently identified major tumor suppressor in ovarian CCC, as well as hepatocyte nuclear factor (HNF)-1b, estrogen receptor (ER), progesterone receptor (PR), and P53. We confirmed that CCC but not PSC had loss of BAF250a expression, HNF-1b up-regulation, loss of ER expression and P53 expression. We further showed that both atypical endometriosis and adjacent CCC had loss of BAF250a expression (38.5% vs. 57.7%), HNF-1b up-regulation (53.8% vs. 92.3%), and loss of ER (84.6% vs. 92.3%) and PR (76.9% vs. 84.6%) expression. Importantly, about 20% of benign ovarian endometriosis had loss of BAF250a expression, 33% with HNF-1b up-regulation, 23% loss of ER expression and 50% loss of PR expression, respectively. The concurrent rate of loss of BAF250a expression, HNF-1b up-regulation, and loss of ER expression was not observed in any benign endometriosis, and was increased to 23.1% in atypical endometriosis, and was further increased to 42.3% in CCC. Therefore, the molecular alterations accumulate in a stepwise manner along the transformation process from benign endometriosis through atypical endometriosis to CCC. These data suggest that a portion of benign ovarian endometriosis has already undergone genetic alterations that lead to aberrant protein expression, possibly conferring a higher risk for malignant transformation.
