ARID1A and endometrioid tumor: PIK3CA and ARID1A mutations were more frequent in clear cell or endometrioid tumors than in other types (6/7 vs. 4/15 and 4/7 vs. 3/15; P = 0.016 and 0.11, respectively), consistent with previous studies of all-age-group ovarian tumors [13, 15, 27].