ARID1A and papillary serous cystadenocarcinoma: In fact, ARID1A under-expression is thought to induce malignant transformation of endometriotic lesions in a stepwise manner, as a gradual loss of ARID1A expression has been observed from benign (20%) to atypical endometriosis (40%) and to OCCC adjacent to endometriosis (58%), the latter also compared with papillary serous carcinoma, where the expression of wild-type ARID1A was conserved [69].