The protein BAF250A encoded by the ARID1A gene is one of the essential subunits of the SWI/SNF chromatin remodeling complex, and in a wide range of tumors, ARID1A is the most commonly mutated subunit in the SWI/SNF complex and one of the most commonly mutated oncogenes in human cancers (23). The gene discussed is ARID1A; the disease is cancer.