Expression of programmed cell death 1 and programmed cell death ligand 1 in extranodal NK/T-cell lymphoma, nasal type.

Programmed cell death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) are new therapeutic targets in cancer immunotherapy. The aim of this study was to investigate the clinicopathological characteristics of PD-1 and PD-L1 expression in extranodal natural killer/T‑cell lymphoma, nasal type (ENKTL). We performed PD-1 and PD-L1 immunostaining in 79 ENKTL biopsy samples and retrospectively analyzed medical records of all 79 patients from four tertiary referral hospitals. The expression of PD-1 and PD-L1 by tumor cells and/or infiltrating immune cells was evaluated. The expression rates of PD-L1 in tumor cells and infiltrating immune cells were 79.7 and 78.5 %, respectively, whereas PD-1 in tumor cells and infiltrating immune cells were 1.3 and 11.4 %. The PD-L1 positivity in tumor cells and infiltrating immune cells was significantly associated with low international prognostic index (IPI) (P = 0.044 and 0.037, respectively). Patients with normal range of serum lactate dehydrogenase demonstrated a significantly higher PD-L1 positivity in tumor cells (P = 0.020). PD-L1-positive patients had a trend toward better overall survival compared with that in patients with PD-L1-negative in tumor cells and infiltrating immune cells (P = 0.498 and 0.435, respectively). The expression rate of PD-L1 was up to 79.7 % in ENKTL, while PD-1 expression rate was very low. This is the first report describing the clinicopathological features and survival outcome according to expression of PD-1 and PD-L1 in ENKTL.