Herein, we investigated the immunohistochemical expression of five subunits (ARID1A, ARID1B, SMARCA2, SMARCA4, and SMARCB1) of the SWI/SNF complex in 21 undifferentiated/dedifferentiated gastric carcinomas, as well as other import immunohistochemical markers, including P53, programmed cell death ligand 1(PD-L1), SOX2, SALL4, and mismatch repair proteins MutL homolog 1 (MLH1), MutS homolog 2 (MSH2), MSH6, and PMS1 homolog, mismatch repair system component 2 (PMS2). The gene discussed is CD274; the disease is gastric carcinoma.