Clinicopathological significance and prognostic role of tumor-infiltrating lymphocytes in colorectal cancer

Purpose: This study aimed to elucidate the clinicopathological significance and prognostic role of tumor-infiltrating lymphocytes in colorectal cancer. Methods: The immunohistochemistry of CD3 and CD8 was performed on 265 human colorectal cancer tissues to investigate the tumor-infiltrating lymphocytes using Immunoscore. The correlation between Immunoscore and clinicopathological characteristics, including survival rates, was elucidated. In addition, the impact of tumor-infiltrating lymphocytes on programmed death-ligand 1 (PD-L1) protein expression was evaluated through immunohistochemistry. Results: Of the 265 colorectal cancer tissues, 40.8% had high Immunoscore, while 59.2% had low Immunoscore. A high Immunoscore was significantly correlated with favorable tumor behaviors, including lower rates of vascular, lymphatic, and perineural invasion; lymph node metastasis; and distant metastasis. PD-L1 expressions of tumor and immune cells were significantly higher in patients with high Immunoscore than in those with low Immunoscore. In addition, colorectal cancer tissues with high CD8-positive lymphocytes showed higher PD-L1 expressions of tumor and immune cells than colorectal cancer tissues with low CD8-positive lymphocytes. There was a significant correlation between high Immunoscore and better overall survival. However, there was no significant difference in survival rate according to PD-L1 expressions of tumor and immune cells in high and low Immunoscore subgroups. Conclusions: Taken together, our results showed that high tumor-infiltrating lymphocytes were significantly correlated with favorable tumor behaviors and better survival. In addition, there was a significant correlation between PD-L1 expression and tumor-infiltrating lymphocytes.