To explore the relationship between the tertiary lymphoid structures (TLSs) and tumor-infiltrating lymphocytes (TILs), and their distribution characteristics as well as the prognostic value in gastric cancer (GC).

Material and methods:
The TLSs and four subtypes of TILs were assessed by immunohistochemical (IHC) staining. The presence of MECA-79 positive high endothelial venules (HEVs) identified among the ectopic lymphocyte aggregation area in the GC tissue was defined as valid TLSs. The number of labeled TILs was observed in 5 fields of the most positive cells in the tumor center, invasive edge and within the TLSs, at a field of vision ×40.

The TLS distribution was significantly higher in the tumor invasive edge than the tumor center (p < 0.001). Similarly, the infiltrating density of CD8+T cells and GrB+T cells was statistically significantly higher in the tumor infiltrating edge than the tumor center. The total number of TILs and FOXP3+T cells showed a contrary distribution. There was a positive correlation of the density of TLSs and TILs with both the location and the immune phenotype. A higher frequency of TILs and TLSs is often associated with favorable clinicopathologic parameters. Higher numbers of peri-TLSs (p = 0.007), peri-CD8+(p = 0.019) and peri-GrB+TILs (p = 0.032) were significantly correlated with the favorable overall survival. Multivariate analysis revealed that the densities of TILs (p = 0.019) and TLSs (p = 0.037) were independent prognostic predictor for GC patients.

We provide evidence that TLSs were positively associated with lymphocyte infiltration in GC. Thus, the formation of TLSs predicts advantageous immune system function and can be considered as a novel biomarker to stratify the overall survival risk of untreated GC patients.