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 × 10 9 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.