Prognostic Impact of PD-L2 Expression and Association with PD-L1 in Patients with Small-cell Lung Cancer

Background/Aim: Although some previous studies suggested that programmed cell death-ligand 1 (PD-L1) expression was significantly associated with a favorable postoperative prognosis in patients with small-cell lung cancer (SCLC), the prognostic significance of PD-L2 expression remains unknown. The aim of the current study was to investigate the prognostic significance of PD-L2 expression in patients with SCLC. Patients and Methods: Thirty-eight patients who underwent resection of SCLC were analyzed. A monoclonal anti-human PD-Li antibody (clone SP142) and a monoclonal anti-human PD-L2 antibody (clone 176611) were used as the primary antibodies. Cut-off value for PD-L1 and PD-L2 expression was set to 1%. Results: Among 38 patients, 15 (39.5%) were positive for PD-L2 expression. No significant associations between PD-L2-positivity and clinicopathological factors, including PD-L1 positivity or prognosis were identified. No significant differences in disease-free survival and overall survival were observed between PD-L2-positive patients and PD-L2-negative patients (p=0.367 and p=0.726, respectively). Conclusion: PD-L2 expression is not related to clinicopathological factors or postoperative prognosis in patients with SCLC, though this should be further investigated in studies involving larger populations.