Thoracic mesenchymal malignant tumors and programed cell death ligand‐1 status: Clinicopathologic and prognostic analysis of eight pulmonary sarcomatoid carcinomas and eight malignant mesotheliomas

BACKGROUND: The current study aimed to evaluate the significance of clinicopathological factors, particularly the immunohistochemistry of programed cell death ligand‐1 (PD‐L1), in eight cases each of pulmonary sarcomatoid carcinoma (PSC) and malignant pleural mesothelioma (MPM) at our hospital. METHODS: From January 2004 to December 2020, a total of 16 consecutive patients (eight with PSC and eight with MPM diagnosed via surgical resection or biopsy) were included in this study. After retrospectively reviewing the patient characteristics, the associations between PD‐L1 status and age, sex, stage, histological type, and prognosis were investigated. RESULTS: PD‐L1‐positive staining was observed in four (50%) PSC cases and one (12.5%) MPM case. Among the four PD‐L1‐positive PSC cases, two showed high PD‐L1 expression in the vimentin‐positive sarcomatoid compartment. Moreover, among those with PSC, two survived for about 10 years, whereas the others died within 5 years. No clear correlation was found between PD‐L1 expression and prognosis. Among the patients with MPM, four survived for more than 2 years, with the longest being 9 years. Among MPM cases who received nivolumab, one patient with positive PD‐L1 staining in the sarcomatoid survived, whereas the other with negative PD‐L1 staining did not. CONCLUSION: The present study showed that sarcomatoid carcinoma had a higher PD‐L1 expression compared to non‐small‐cell lung cancer and that both PSC and MPM tended to exhibit PD‐L1 positivity in the sarcomatoid compartment. Moreover, while immune checkpoint inhibitors may somewhat prolong the prognosis of both tumors, further studies with a larger cohort are necessary to confirm our results.