ARID1A and gastric cancer: We aimed to test the following hypotheses: (1) SMARCA4 and SMARCE1 are differentially expressed in GC and show intratumoral heterogeneity; (2) The expression of SMARCA4 and SMARCE1 correlates with clinicopathological patient characteristics, including EBV, MSI, and ARID1A status, (3) SMARCE1 is co‐amplificated with HER2.