Chemoradiation-Induced Alteration of Programmed Death-Ligand 1 and CD8⁺ Tumor-Infiltrating Lymphocytes Identified Patients With Poor Prognosis in Rectal Cancer: A Matched Comparison Analysis

Purpose To evaluate chemoradiotherapy (CRT)-induced changes in the expression levels of programmed death-ligand 1 (PD-L1) and CD8⁺ tumor-infiltrating lymphocytes (TILs) and prognostic associations in rectal cancer. Methods and Materials We performed a paired analysis using pre-CRT biopsies and the corresponding post-CRT resected tissues of 123 rectal cancer patients undergoing preoperative CRT followed by surgery between 2005 and 2012. Immunohistochemistry of PD-L1 and CD8 was analyzed for the specimens. Results The expression levels of PD-L1 and density of CD8⁺ TILs increased after CRT (P<.001 for both). With cutoffs using each median value, sustained higher expression of PD-L1 at pre- and post-CRT (high-to-high) was associated with less increase in the density of CD8⁺ TILs (P=.020). Patients representing sustained high-to-high PD-L1 expression had poorer overall survival and disease-free interval on univariate Kaplan-Meier analysis (P=.018 and.029, respectively), with inferior disease-free interval in low-to-low density CD8⁺ TILs (P=.010). On multivariate analysis, 2 subgroups with high baseline PD-L1 expression level, the high-to-low and high-to-high alterations, showed worse overall survival (hazard ratio 8.34, 95% confidence interval 1.85-37.53 and hazard ratio 11.03, 95% confidence interval 2.33-52.29, respectively), with the highest mortality risk observed in the high-to-high group. Conclusions This study verified the CRT-induced immunologic shift toward increases in PD-L1 expression and density of CD8⁺ TILs in rectal cancer patients. The alteration profiles of checkpoint-related molecules identified the patients with poor prognosis, suggesting potential candidates who can benefit from combining CRT and checkpoint inhibitors.