The prognostic value of tumor-infiltrating lymphocytes in colorectal cancer differs by anatomical subsite: a systematic review and meta-analysis

PurposeIn colorectal cancer (CRC), whether the immune score can be used to predict the clinical prognosis of the patient has not been completely established. Besides, the prognostic values of tumor-infiltrating lymphocytes (TILs) in different anatomical locations, counting sites, and subtypes have been controversial. The purpose of this meta-analysis is to analyze and determine the prognostic value of TILs indices including TIL subsets, infiltrating sites, and anatomical sites.MethodsRelevant literature was obtained by searching PubMed and Google Scholar. The pooled hazard ratio (HR) of the overall survival (OS), disease-free survival (DFS), and cancer-specific survival (CSS) was computed to investigate the prognostic significance of CD3+, CD8+, CD45RO+, and FOXP3+ T cells.ResultsA total of 22 studies involving 5108 patients were included in the meta-analysis. In CC, based on T cell subtypes analysis, the final results indicated that CD8+ and FOXP3+ infiltrating cells, but not CD3+ T cells were prognostic markers for DFS and OS. In addition, with regard to the counting location of TILs, subgroup analysis revealed that only high FOXP3+ infiltrates in the tumor stroma (ST) were significantly associated with OS (HR=0.38, 95% confidence interval (CI)=0.22-0.67, P=0.0007), whereas in invasive margin (IM), high density of CD3+ infiltrating cells indicated increased DFS (HR=0.76, 95% CI=0.62-0.93, P=0.008). At the tumor center (TC), high CD8+ T cells infiltration was associated with improved DFS (HR=0.50, 95% CI=0.38-0.65, P<0.00001). In RC, whether CSS or OS, high-density TIL was associated with improved prognosis.ConclusionIn a single counting site, high-density TILs reflect favorable prognostic value in CC or RC. For CC, more prospective studies are needed to verify whether different anatomical sites affect the distribution of TILs and thus the prognosis of patients. For RC, further studies should analyze the prognostic value of the immune score.