Of the 34 undifferentiated carcinomas examined, 17 (50%) exhibited SWI/SNF complex inactivation, with 11 tumors showing complete loss of both ARID1A and ARID1B, 5 showing complete loss of BRG1 and 1 showing complete loss of INI1.
In summary, expression of claudin-4 is highly specific for true epithelial differentiation and may be useful to distinguish SWI/SNF complex-deficient undifferentiated carcinomas from sarcomas with epithelioid morphology.