Prognostic Associations of BMI and Metabolic Syndrome With Outcomes After Anti-PD-1 Therapy in Recurrent or Metastatic Nasopharyngeal Carcinoma.

To evaluate the associations of body mass index (BMI) and metabolic syndrome (MetS) with outcomes in patients with recurrent or metastatic nasopharyngeal carcinoma (R/M-NPC) receiving anti-PD-1 therapy, and to develop a prognostic model for overall survival (OS). This multicenter retrospective study included 238 patients with BMI ≥ 18.5 kg/m2 from two Chinese hospitals. BMI and MetS associations were evaluated using center-adjusted, center-stratified, hierarchical, and quantitative sensitivity analyses. An OS nomogram was developed in the Xiangya cohort and externally evaluated in the Harbin cohort. In clinical confounder-adjusted models with the exposures entered separately, high BMI was associated with OS (HR, 0.462; 95% CI, 0.324-0.657) and PFS (HR, 0.511; 95% CI, 0.380-0.688), and MetS was associated with OS (HR, 0.433; 95% CI, 0.278-0.674) and PFS (progression-free survival) (HR, 0.616; 95% CI, 0.439-0.866). When BMI and MetS were jointly modelled, the MetS-PFS association was attenuated (HR, 0.714; 95% CI, 0.504-1.012; p = 0.058). Exploratory biomarker analyses revealed group differences in combined positive score (CPS) and pan-immune-inflammation value (PIV). Center-specific effect directions were consistent, but the external-center calibration slope was 0.53 (95% CI, 0.08-0.98). Among anti-PD-1-treated Chinese patients with R/M-NPC and a BMI ≥ 18.5 kg/m2, higher BMI and MetS showed prognostic associations. These observational data do not establish causal or treatment-predictive effects, and prospective validation in non-Chinese populations across the full body-weight spectrum is needed.