Radiation-induced lymphopenia correlates with survival in nasopharyngeal carcinoma: Impact of treatment modality and the baseline lymphocyte count

Background and purpose: We evaluated the relationship between patient-, tumor-, and treatment-related features and radiation-induced lymphopenia (RIL) and evaluated the correlation between RIL and survival outcome in NPC patients to help improve the treatment strategy. Methods: This retrospective study included 374 patients with stage II-IVa NPC who had been treated with definitive RT and were enrolled from 2004 to 2015; The associations between the G3-4 RIL (absolute lymphocyte count, ALC < 0.5 × 10⁹ cells/L) during RT and patient-, tumor-, and treatment-related factors were assessed using Cox regression analyses. The correlation between ALC nadir and survival was examined using a Kaplan-Meier analysis, compared with the log-rank test, and confirmed by a Cox proportional hazards analysis. Results: In the multivariate analysis, lower baseline ALC and intensity modulated radiation therapy (IMRT) (vs. 2 dimensional-conformal radiation therapy,2D-CRT) were identified as 2 independent factors that were associated with G3-4 RIL. In the multivariate survival analysis, patients with G3-4 ALC nadir had longer local recurrence-free survival durations (LRFS) (vs. G0-2 nadir, HR = 0.548, P = 0.005) and longer progression-free survival durations (PFS) (vs. G0-2 nadir, HR = 0.676, P = 0.022), while patients with G4 ALC nadir had a shorter distant-metastasis-free survival duration (DMFS) (vs. G0-2 nadir, hazard ratio [HR] = 2.567, P = 0.037). Conclusions: In the study, lymphopenia during RT were affected by baseline ALC and RT modality independently. Moreover, G3-4 ALC nadir was independently linked with longer PFS and LRFS durations, while G4 ALC nadir was independently linked with a shorter DMFS duration.