ARID1A and endometriosis: Studies examining BAF250a expression by IHC show that in just over half of the reported cases of EAOC, loss of BAF250a expression is seen the majority of the time (67–80%) in areas of contiguous endometriosis or atypical endometriosis (see Figure 1), and that a loss of Baf250a protein expression seemed to be an early molecular event in the development of Baf250a-negative EAOC [42, 95, 118].