In malignant pleural mesothelioma (MPM) and pulmonary sarcomatoid carcinoma (PSC), which are thoracic mesenchymal malignant tumors, programed cell death ligand‐1 (PD‐L1) was positive in the vimentin‐positive part or the sarcomatoid area, found to be clinicopathologically significant. The gene discussed is CD274; the disease is pancreatic serous cystadenoma.