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 smallcell lung cancer (SCLC), the prognostic significance of PDL2 expression remains unknown. The aim of the current study was to investigate the prognostic significance of PDL2 expression in patients with SCLC. Patients and Methods: Thirty-eight patients who underwent resection of SCLC were analyzed. A monoclonal anti-human PD-L1 antibody (clone SP142) and a monoclonal anti-human PDL2 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.