ARID1A and undifferentiated ovarian carcinoma: In a multi‐institutional cohort study [37] of 23 cases of dedifferentiated and undifferentiated ovarian carcinomas (DDOC/UDOC), 18 out of 22 cases with interpretable immunohistochemical results showed loss of expression of core SWI/SNF proteins, with 10 cases exhibiting substantial loss of ARID1A and ARID1B.