Severe Lymphopenia Predicts Poorer Survival in Patients With Rectal Cancer Undergoing Neoadjuvant Chemoradiation.

Purpose: Chemoradiation-induced lymphopenia is common and associated with poorer survival in multiple solid malignancies. However, the association between chemoradiation-related lymphopenia and survival outcomes in rectal cancer is yet unclear. The objective of this study was to evaluate the prognostic impact of lymphopenia and its predictors in patients with rectal cancer undergoing neoadjuvant chemoradiation.

Methods: The inclusion criteria for this single-institution retrospective study were as follows: (1) biopsy-proven diagnosis of rectal adenocarcinoma, (2) receipt of neoadjuvant chemoradiation followed by surgery, and (3) absolute lymphocyte count available prior to and within 12 weeks of chemoradiation. In general, chemoradiation consisted of 5-fluorouracil or capecitabine and radiotherapy with 50.4 Gy over 28 fractions. Lymphopenia was graded according to the Common Terminology Criteria for Adverse Events version 5.0. The primary variable of interest was absolute lymphocyte count nadir within 12 weeks of chemoradiation, dichotomized by <500/μL (grade 3 or worse lymphopenia). The primary endpoint was overall survival. Cox modeling and Kaplan-Meier methods were used to perform survival analyses.

Results: A total of 193 patients were identified with a median follow-up of 68 months. Overall clinical stage was 2 in 21% and 3 in 76%. Median baseline lymphocyte count for the entire cohort was 1700/μL. One hundred ten patients (57%) experienced chemoradiation-related severe lymphopenia. Pathologic complete response rate was 21%; 83% received adjuvant chemotherapy. Lower baseline lymphocyte count was significantly associated with increased risk for chemoradiation-related severe lymphopenia (odds ratio, 1.71). On multivariable Cox regression analysis, chemoradiation-related severe lymphopenia was significantly associated with worse disease-free survival (hazard ratio, 2.64) and overall survival (hazard ratio, 4.32). Five-year overall survival was 79% versus 92%, and 5-year disease-free survival was 70% versus 86% in the cohort that experienced versus did not experience severe lymphopenia, respectively.

Discussion: Chemoradiation-induced lymphopenia is common and a prognostic marker of poorer survival in rectal cancer. Closer observation in high-risk patients and treatment modifications may be potential approaches to mitigating treatment-related lymphopenia. Our findings also suggest an important role of the host immunity in rectal cancer outcomes and support future studies investigating ways to reduce treatment-induced lymphopenia.