ARID1A and neoplasm: Furthermore, studies discovered that ARID1A mutations and loss of BAF250a protein accumulated in a stepwise manner during the transformation process from benign endometriosis through atypical endometriosis to OCCC, suggesting that ARID1A mutation occurred as a very early event in OCCC development (Yamamoto et al., 2012a; Xiao et al., 2012).