Prognostic value of tumor infiltrating lymphocytes combined with PD-L1 expression for patients with solitary colorectal cancer liver metastasis

Background: The aim of this study was to assess the prognostic value of CD8+ tumor infiltrating lymphocytes (TIL) combined with programmed cell death-ligand 1 (PD-L1) expression for patients with solitary colorectal cancer liver metastasis (SCLM) undergoing R0 resection Methods: Patients undergoing curative hepatectomy for SCLM were reviewed. Immunohistochemical multiplex technique was used for quantifying CD8+ TIL, and immunohistochemical staining was used for assessing PD-L1 expression. The tumor immune microenvironment (TIME) was classified as strong for high CD8+ TIL and low PD-L1, weak for low CD8+ TIL and high PD-L1, and mild for the rest. Recurrence-free survival (RFS) and overall survival (OS) was compared between these groups. Results: Among the 94 patients included, a high CD8+ TIL and high PD-L1 expression was observed in 51 (54.3%) and 47 (50.0%) patients, respectively. Strong, mild, and weak TIME was observed in 24 (25.5%), 42 (44.7%), and 28 (29.8%) patients, respectively. Patients with a high CD8+ TIL had a significant longer RFS than patients with a low CD8+ TIL (3-year RFS rate, 71.6% vs. 55.3%, P=0.018). The 3-year RFS rate in the strong TIME group was significantly higher than that in the mild and weak TIME groups (89.5% vs. 71.7% and 28.8%, P<0.001), as was the 3-year rate of OS (93.8% vs. 81.8% and 61.6%, P<0.001). CD8+ TIL combined with PD-L1 expression showed better predicting accuracy for RFS than CD8+ TIL alone. Conclusions: The density of CD8+ TIL combined with PD-L1 expression in liver metastasis was a predictor of RFS for patients with SCLM undergoing R0 resection, and therefore can be used for guiding the postoperative treatment of these patients.