Abstract: Objective To investigate the prognostic value of absolute lymphocyte count (ALC) in patients with natural killer/T⁃cell lymphoma (NKTCL) treated with programmed death⁃1 (PD⁃1) inhibitor, and to develop a prognostic model for predicting progression⁃free survival (PFS). Methods A cohort of 41 patients with NKTCL who underwent PD⁃1 inhibitor combination therapy at Beijing Tongren Hospital, Capital Medical University from June 2019 to June 2023 were enrolled. The optimal cut⁃off value for ALC was determined using the maximum selected rank statistics. The Cox proportional hazards regression model was used to analyze the correlation between ALC and prognosis, and a prognostic scoring model was constructed based on the identified prognostic factors. Results The optimal cut⁃off value of ALC was 1.35×10⁹/L. Significant differences in PFS and overall survival (OS) were observed between the low ALC group and high ALC group (P<0.001). The median PFS and median OS in the high ALC group were 216 days and 343 days, respectively, whereas both median PFS and OS were not reached in the low ALC group. Multivariable analysis demonstrated that ALC ≥1.35×109/L was an independent prognostic factor for PFS (HR=3.185, 95%CI: 1.146-8.851). The scoring model constructed based on age, disease status, Ann Arbor staging system and ALC could effectively distinguish low⁃risk from high⁃risk patients, with an area under the curve (AUC) of 0.924 for predicting PFS, which was significantly higher than that of the conventional nomogram⁃revised risk index (NRI) score (0.545, P<0.001). The clinical benefit rate (CBR) of the low⁃risk group reached 83.3%, significantly exceeding the 43.5% observed in the high⁃risk group (P=0.012). Conclusions Pretreatment ALC is an independent prognostic factor for PFS in NKTCL patients receiving PD⁃1 inhibitor combination therapy. The novel prognostic model integrating age, disease status, Ann Arbor stage and ALC improves risk stratification and may inform individualized treatment strategies.

Key words: NK/T cell lymphoma, PD?1 monoclonal antibody, Absolute lymphocyte count, Prognostic factor, Prognostic model