Abstract
BACKGROUND: To investigate the association between absolute lymphocyte count (ALC) nadir and survival outcomes in esophageal squamous cell carcinoma (ESCC) patients who received definitive chemoradiotherapy (CRT) combined with anti-PD-1 immunotherapy, as well as to explore clinical characteristics and dosimetric parameters that affect ALC nadir during CRT. PATIENTS AND METHODS: Patients with ESCC (n = 602) who underwent definitive CRT were analyzed, of whom 166 received combined anti-PD-1 immunotherapy and CRT. Changes in ALC and survival were compared between patients with and without immunotherapy. Propensity score matching (PSM) was performed to minimize the effects of confounding factors. Low ALC was defined as nadir of <0.33 × 103 cells/μL during CRT (top tertile). Univariate and multivariate logistic regression were used to identify predictors of low ALC nadir. RESULTS: Patients with immunotherapy had significantly higher ALC in the first 3 weeks during CRT and higher ALC nadir than those without. Overall survival was more favorable in patients with immunotherapy both before and after PSM. After a median follow-up of 12.1 months, patients with low ALC during CRT had a worse progression-free survival (PFS) (P = .026). In multivariate analysis, low ALC remained a significant prognostic factor for PFS. Planning target volume (PTV) and heart V5 were revealed to be independent predictors of low ALC. CONCLUSIONS: The addition of anti-PD-1 immunotherapy to definitive CRT could mitigate the decline of ALC during radiotherapy and might prolong survival. Low ALC nadir was correlated to worse PFS, larger PTV, and higher heart V5 in patients receiving combined immunotherapy and CRT.