ARID1A and ovarian endometrioid adenocarcinoma: As above discussed, both clear cell ovarian cancer and endometrioid ovarian cancer harbor ARID1A loss-of-function mutations (occurring in 50% and 30% of cases, respectively), accompanied by PTEN loss and mutations in PI3KCA, KRAS, CTNNB1, PPP2R1A and TERT promoter, and by additional molecular defects, such as mismatch-repair deficiency, hypermutation and microsatellite instability.