ARID1A and neoplasm: Among dozens of SWI/SNF complex genes, ARID1A, ARID1B, ARID2, SMARCA4, and PBRM1 have been reported to be altered in  ≥ 5% of a certain tumor and are mutated above the background mutation rate in two or more cancer types, accounting for their gene length, which suggests that mutations in these genes are “driver” rather than “passenger” variations [7].