Unique distribution of programmed death ligand 1 (PD-L1) expression in East Asian non-small cell lung cancer

Background: To determine the proportion and clinical features of programmed death ligand 1 (PD-L1) expression in East Asian non-small cell lung cancer (NSCLC). Methods: PD-L1 expression was assessed by immunohistochemistry (IHC) and tumor proportion score (TPS) with the use of PD-L1 IHC 22C3 antibody (Dako North America) in 108 surgically resected lung squamous cell carcinomas (SCC) and 221 lung adenocarcinomas (LUADs), and was correlated with clinical variables, histologic subtypes, and common driver mutations. Results: Positive PD-L1 expression was found in 37 lung SCC (37/108, 34.3%), including 15 cases with TPS >= 50% (15/108, 13.9%) and 22 cases with TPS <50% (22/108, 20.4%). In adenocarcinoma cohort, 9 cases were found PD-L1 expression positive (9/221, 4.1%), including 1 case with TPS >= 50% (1/221, 0.5%) and 8 cases with TPS < 50% (8/221, 3.9%). Totally, high PD-L1 expression (TPS >= 50%) was significantly associated with male sex (P=0.026), current/ever smoking history (P=0.008) and SCC subtype (P<0.001). Positive PD-L1 expression (including TPS >= 50% and TPS < 50%) in LUAD cohort was significantly associated with male sex (P=0.046), current/ever smoking history (P=0.002), mutation pan-negative status (P=0.038), solid-predominant subtype (P<0.001), large tumor size (P=0.027) and lymph node metastasis (P=0.019). No significant difference was found between PD-L1 high expression group (TPS >= 50%) and low/negative expression group in SCC cohort. Conclusions: This study revealed the unique distribution of PD-L1 expression in East Asian NSCLCs, which is largely different from Western populations. Since the high response rate of pembrolizumab in the treatment of lung cancer patients with PD-L1 TPS >= 50%, this result indicates that prospective PD-L1 expression testing in specific East Asian patients could facilitate decision making for immunotherapy.