ARID1A and breast cancer: The frequency of ARID1A alterations by cancer type is as follows (Figure 1A): endometrial cancer, 21.3% of patients; bladder cancer, 12.9%; gastric cancer, 11% (the latter includes gastric/GE junction for cfDNA); cholangiocarcinoma, 10.9%; hepatocellular carcinoma, 10.6%; carcinoma of unknown primary, 8.5%; cervical cancer, 7.2%; breast cancer, 6.1%; head and neck cancer, 5.3%; colorectal cancer, 5%; pancreatic cancer, 4.5%; and lung cancer, 3.9%.