Significance of Programmed Cell Death-Ligand 1 Expression and its Association with Survival in Patients with Small Cell Lung Cancer

Background: Programmed cell death 1 receptor-ligand interaction is a major pathway often hijacked by tumors to suppress immune control. The aim of this retrospective study was to investigate the prevalence and prognostic roles of programmed cell death -ligand 1 (PD-L1) expression in small cell lung cancer (SCLC). Methods: The expression of PD-L1 was evaluated by immunohistochemical analysis in 102 specimens of SCLC. Tumors with staining in over 5% of tumor cells were scored as positive for PD-L1 expression. Survival analysis was performed using the Kaplan-Meier method. Results: Expression of PD-L1 in tumor cells was observed in 71.6% (73 of 102) of SCLCs, and was significantly correlated with a limited disease (LD) stage. SCLC patients with PD-L1-positive tumors showed significantly longer overall survival (OS) than those with PD-L1-negative (median OS, 16.3 versus 7.3 months; p < 0.001, respectively). Multivariate analyses demonstrated that a good performance status, LD stage, and expression of PD-L1 were significantly predictive of better OS, independently of other factors. We found no relevance between PD-L1 expression and progression-free survival for first-line treatment in LD- and extensive disease-SCLC patients. Conclusions: In patients with SCLC, expression of PD-L1 is positively correlated with a LD stage, and is independently predictive of a favorable outcome.