Investigating the Role of Tumor-Infiltrating Lymphocytes as Predictors of Lymph Node Metastasis in Deep Submucosal Invasive Colorectal Cancer: A Retrospective Cross-Sectional Study

SIMPLE SUMMARY: In advanced colorectal cancer (CRC), tumor-infiltrating T cells (TILs) are reportedly associated with lymph node (LN) metastasis and prognosis. However, there are no reports focusing on early-stage CRC or examining changes in TILs according to the degree of CRC invasion. Therefore, we investigated the relationship between LN metastasis and TILs in early-stage CRC using the triple immunofluorescence method for CD4, CD8, and Foxp3. We also examined changes in TILs during invasion from early-stage CRC to advanced CRC. We found that a higher number of Foxp3+ T cells and higher Foxp3/CD4 and Foxp3/CD8 ratios at the invasive front of the tumor were associated with LN metastasis. Furthermore, tumor invasion was positively correlated with the number of TILs in CRC. This study provides new predictors of LN metastasis in T1b CRC and provides insight into the tumor microenvironment in CRC invasion. ABSTRACT: The role of tumor-infiltrating T cells (TILs) in colorectal cancer (CRC) and their significance in early-stage CRC remain unknown. We investigated the role of TILs in early-stage CRC, particularly in deep submucosal invasive (T1b) CRC. Sixty patients with CRC (20 each with intramucosal [IM group], submucosal invasive [SM group], and advanced cancer [AD group]) were randomly selected. We examined changes in TILs with tumor invasion and the relationship between TILs and LN metastasis risk. Eighty-four patients with T1b CRC who underwent initial surgical resection with LN dissection or additional surgical resection with LN dissection after endoscopic resection were then selected. TIL phenotype and number were evaluated using triple immunofluorescence for CD4, CD8, and Foxp3. All subtypes were more numerous according to the degree of CRC invasion and more abundant at the invasive front of the tumor (IF) than in the center of the tumor (CT) in the SM and AD groups. The increased Foxp3 cells at the IF and high ratios of Foxp3/CD4 and Foxp3/CD8 positively correlated with LN metastasis. In conclusion, tumor invasion positively correlated with the number of TILs in CRC. The number and ratio of Foxp3 cells at the IF may predict LN metastasis in T1b CRC.