Investigating tumor-infiltrating lymphocytes as predictors of lymph node metastasis in deep submucosal invasive esophageal squamous cell carcinoma: a retrospective cross-sectional study.

BACKGROUND: Various subtypes of tumor-infiltrating lymphocytes (TILs) are associated with prognosis in various cancer types. In esophageal squamous cell carcinoma (ESCC), TILs have been associated with prognosis in advanced stages of the disease. However, their significance in superficial esophageal squamous cell carcinoma (SESCC) remains unknown. In this study, we investigated the role of TILs in SESCC. METHODS: First, we included 212 SESCC lesions with a diameter of 10-20 mm (65 pT1a-EP, 74 pT1a-LPM,40 pT1a-MM, and 33 pT1b-SM lesions) that were resected at our hospital from November 2007 to December 2019. We then examined changes in TILs related to tumor invasion. We evaluated the phenotype and number of TILs using triple immunofluorescence staining for CD4, CD8, and FoxP3. In addition, we selected 97 consecutive pT1b-SM lesions treated during the same period. These specimens were used to examine the association between TILs and lymph node metastasis (LNM) in pT1b-SM cases. RESULTS: The number of CD4 + , CD8 + , and FoxP3 + TILs infiltrating the tumor increased significantly with increasing invasion depth. In pT1b-SM lesions, CD4 + , CD8 + , and FoxP3 + TIL counts were significantly higher in the invasive front (IF) than in the tumor center (CT). Moreover, in patients undergoing surgical resection or endoscopic submucosal dissection (regardless of additional chemoradiotherapy), the number and ratio of FoxP3 + TILs in IF were significantly higher in patients with LNM than in those without, suggesting their potential utility as predictive biomarkers. CONCLUSIONS: The number and ratio of FoxP3 + TILs in the IF may be an indicator of LNM risk in SESCC.