ARID1B and carcinoma: Recently, it has been suggested that the highly aggressive behavior of undifferentiated/dedifferentiated carcinomas may be due to mutations in proteins of the SWI/SNF complex (ARID1B, SMARCA4/BRG1, SMARCB1/INI1), which occur in about two‐thirds of cases18, 45, 47; the loss of these proteins on immunohistochemistry seems to be a specific diagnostic marker of undifferentiated/dedifferentiated carcinoma.48