ARID1A, which encodes the BAF250a subunit of the SWI/SNF complexes, is reported to be a tumour suppressor gene that is frequently inactivated by frameshift or truncating mutations, resulting in a lack of protein expression in numerous human cancers, for example ovarian clear cell carcinoma, gastric cancer, HCC, breast cancer, pancreatic cancer, bladder cancer and colon cancer.67, 68, 69, 70, 71, 72, 73. Here, ARID1A is linked to breast cancer.