ARID1A and endometrioid adenocarcinoma: In 3 out of the 6 OEM from iPAD mice, Pax8-positive cells in OEM partially lacked the expression of both Pten and Arid1a and showed cellular stratification, a cribriform structure, and stromal invasion with prominent nuclear atypia, corresponding to endometrioid carcinoma (Fig. 3C,D).