Programmed death-1 ligand 1 and 2 are highly expressed in pleomorphic carcinomas of the lung: Comparison of sarcomatous and carcinomatous areas.

Pleomorphic carcinoma (PC) of the lung is a rare type of poorly differentiated non-small cell lung carcinoma (NSCLC) that belongs to sarcomatoid carcinoma (SC). It exhibits aggressive behaviour and resistance to chemotherapy and radiotherapy. Recently, immunotherapy targeting the programmed death-1 (PD-1)/PD ligand 1 (PD-L1) pathway has demonstrated favourable clinical outcomes in NSCLC. However, the expression patterns of PD-1-related molecules in pulmonary PC remain elusive. PD-L1 and PD-L2 expression was estimated in 41 cases of PC using immunohistochemistry. CD8(+) and PD-1(+) tumour-infiltrating lymphocytes (TILs) were also evaluated. PD-L1 and PD-L2 were highly expressed in pulmonary PCs (90.2% [37/41)]; 87.8% [36/41]). The amount of CD8(+) or PD-1(+) TILs and the ratio of PD-1(+)/CD8(+) TILs in PC were higher in males, smokers and older patients. PD-L1-positive PCs were infiltrated by higher numbers of CD8(+) TILs compared to PD-L1-negative cases (P=0.006). Of note, PD-L1 expression in pulmonary PCs was significantly higher in sarcomatous areas than in the carcinomatous portion (P=0.006). PC patients with a high ratio of PD-1(+)/CD8(+) TILs showed a shorter progression-free survival (P=0.036), whereas PD-L1 and PD-L2 expression had no prognostic implications. Our study demonstrates that pulmonary PCs very frequently express PD-L1 and PD-L2. Moreover, their expression is higher in sarcomatous cells than in carcinomatous areas. Thus, targeting the PD-1/PD-L1 pathway may represent a potential therapeutic candidate for this aggressive tumour.