The Immunoscore is a Superior Prognostic Tool in Stages II and III Colorectal Cancer and is Significantly Correlated with Programmed Death-Ligand 1 (PD-L1) Expression on Tumor-Infiltrating Mononuclear Cells.

Abstract

In colorectal cancer (CRC), the indication for immune checkpoint inhibitors is determined by the microsatellite instability status of the tumors. However, an optimal biomarker for their indication has not been fully identified to date. This study aimed to establish the clinicopathologic importance of the Immunoscore (IS) in CRC and to clarify the relationships between the IS, programmed death-ligand 1 (PD-L1) expression, and tumor-associated macrophages. In 132 cases, CRC was diagnosed and surgically treated in our department from 2009 to 2010. Immunohistochemical staining using primary antibodies PD-L1, CD3, CD8, CD68, and CD163 was performed. The IS was determined according to the proposal of an international task force. Statistical analyses were performed to investigate the correlation between the IS, clinicopathologic variables, and expression of immune checkpoint molecules. The overall survival (OS) and relapse-free survival (RFS) in the high-IS group (I3-4) were significantly better than in the low-IS group (I0-2) (OS: P = 0.0420; RFS: P = 0.0226). The positivity rate for PD-L1 on tumor cells (tPD-L1) was only 0.8%, whereas that for PD-L1 on interstitial tumor-infiltrating mononuclear cells (iPD-L1) was 18.2%. The iPD-L1-positive group showed significantly better survival in terms of both OS and RFS than the iPD-L1-negative group (OS: P = 0.0278; RFS: P = 0.0253). The findings showed significant correlation between the IS and iPD-L1 expression (P < 0.0001). The study found that a high IS was a good indicator of a better prognosis and significantly correlated with iPD-L1 expression in CRC.