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.