Prognostic Significance of Tumor-infiltrating Lymphocytes on Survival Outcomes of Patients With Resected Pancreatic Ductal Adenocarcinoma: A Systematic Review and Meta-Analysis

Tumor-infiltrating lymphocytes (TILs) play an important role in mediating treatment response in pancreatic cancer. This meta-analysis investigated the prognostic significance of TIL subsets on overall survival (OS) and disease-free survival (DFS) of patients with pancreatic cancer. Studies were gathered via search of PubMed, Google Scholar, and Cochrane Library databases up to August 1, 2019. Using Review Manager version 5.3.5, pooled hazard ratios and 95% confidence intervals (CIs) were calculated using random or fixed-effects models, depending on the heterogeneity of studies. A total of 11 studies comprising 1760 patients were included in the meta-analysis. Pooled analysis revealed that high CD8(+) TILs were associated with improved OS [hazard ratio (HR)=0.59, 95% CI=0.51-0.69, P<0.00001] and DFS (HR=0.60, 95% CI=0.50-0.73, P<0.00001). Similarly, high CD3(+) TILs correlated with better OS (HR=0.64, 95% CI=0.54-0.75, P<0.00001) and DFS (HR=0.53, 95% CI=0.31-0.92, P<0.0001). In contrast, high FoxP3(+) TILs were associated with worse OS (HR=1.39, 95% CI=1.03-1.88, P=0.03). Finally, high CD4(+) TILs showed significant improvement in OS (HR=0.74, 95% CI=0.63-0.86, P=0.0001). TILs are a promising prognostic biomarker in pancreatic cancer. Prospective studies evaluating TILs are recommended as well as the establishment of standards in the assessment of TILs.