Expression of PD-1 and PD-L1 on Tumor-Infiltrating Lymphocytes Predicts Prognosis in Patients with Small-Cell Lung Cancer

Introduction Immune therapy has shown good results in small-cell lung cancer (SCLC), but the impact of immune microenvironment of the disease is unclear. In this work, we detected expression of programmed death 1 (PD-1), PD-ligand 1 (PD-L1), and other immune biomarkers of cancer. We also analyzed the correlations between these markers and survival in SCLC. Patients and Methods Protein expression of PD-1, PD-L1, PD-L2, CD3, CD4, CD8, and FOXP3 was analyzed in surgical tissues from 102 SCLC patients by immunohistochemistry. Results Positive expression of PD-1 on tumor-infiltrating lymphocytes (TILs) was found in 40.2% of patients; 37.3% of patients showed positive expression of PD-L1 on TILs; and 3.9% showed positive expression of PD-L1 on tumor cells. PD-L2 protein was not expressed on tumor cells or TILs. Survival analysis showed that positive expression of PD-L1 on TILs was correlated with longer relapse-free survival (RFS) (p=0.004). Positive expression of PD-1 combined with a high ratio of lymphocytes (CD3, p=0.004; CD4, p=0.011; CD8, p=0.009; FOXP3, p=0.009) was associated with significantly better RFS than negative expression of PD-1 combined with a lower ratio of lymphocytes. Positive expression of PD-L1 combined with a high ratio of lymphocytes (CD3, p<0.001; CD4, p=0.001; CD8, p=0.002; FOXP3, p=0.001) was associated with significantly better RFS than negative expression of PD-L1 combined with a lower ratio of lymphocytes. All patients' stage were between I and III. Conclusion PD-1 and PD-L1 expression might be good prognostic factors in SCLC.