Distinct role of tumor-infiltrating lymphocytes between synchronous and metachronous colorectal cancer

Purpose Tumor-infiltrating lymphocytes (TILs) may influence the prognosis of colorectal liver metastasis (CRLM). We assessed the prognostic value of evaluating TILs in the primary and metastatic sites of synchronous CRLM as well as metachronous CRLM. Methods We examined 90 patients who underwent curative primary and liver metastasis resection for colorectal cancer. CD8 + TILs (cytotoxic T cells) or CD45RO + TILs (memory T cells) in both primary and metastatic sites were simultaneously evaluated by immunohistochemistry. Results Fifty-one patients had synchronous CRLM, and 39 patients had metachronous CRLM. In synchronous cases, the overall survival (OS) was significantly worse in patients with low CD8 + or CD45RO + TILs in a metastatic site than in those with high CD8 + or CD45RO + TILs ( P = 0.017 and P = 0.005, respectively). Multivariate analysis showed that age ≥ 65 years ( P = 0.043), maximum tumor size ≥ 30 mm ( P = 0.003), primary N2-3 ( P = 0.019), and low CD8 + TILs in metastatic site ( P = 0.046) were independent poor prognostic factors. In contrast, in metachronous cases, OS was significantly worse in patients with low CD45RO + TILs in a primary site than in those with high CD45RO + TILs ( P = 0.021). CD45RO + TILs in a primary site ( P = 0.044) were determined to be independent prognostic factor on multivariate analysis. Conclusions The immune microenvironment between synchronous and metachronous CRLM might be different, and these differences may affect its prognosis.