While ARID1A is widely considered a tumor suppressor in the endometrium and more broadly41–44, we show here that ARID1 re-expression in tumors with concomitant ARID1A/ARID1B loss promotes cBAF reassembly and binding at distal enhancers associated with epithelial differentiation and estrogen signaling pathways. Here, ARID1A is linked to neoplasm.