TAMs and PD-1 Networking in Gastric Cancer: A Review of the Literature

Simple Summary This study aims to explore the connection between tumor-associated macrophages (TAMs) and the programmed cell death protein 1(PD-1)/programmed death ligand 1 (PD-L1) pathway in gastric cancer (GC). Immune checkpoint inhibitors (ICIs) have shown promise in cancer treatment. Here, we investigate their potential in GC. TAMs, abundant in the tumor microenvironment (TME), can express PD-1, which interacts with PD-L1 on cancer cells. This systematic review indicates that high PD-L1 expression correlates with increased TAM infiltration and may lead to worse patient outcomes. This suggests that TAMs could be crucial in regulating the PD-1/PD-L1 network in GC. Enhanced comprehension of this intricate relationship may offer opportunities for optimizing the efficacy of ICIs in this malignancy.Abstract Background: Gastric cancer (GC) is one of the most common and aggressive types of cancer. Immune checkpoint inhibitors (ICIs) have proven effective in treating various types of cancer. The use of ICIs in GC patients is currently an area of ongoing research. The tumor microenvironment (TME) also seems to play a crucial role in cancer progression. Tumor-associated macrophages (TAMs) are the most abundant population in the TME. TAMs are capable of displaying programmed cell death protein 1 (PD-1) on their surface and can form a ligand with programmed death ligand 1 (PD-L1), which is found on the surface of cancer cells. Therefore, it is expected that TAMs may significantly influence the immune response related to immune checkpoint inhibitors (ICIs). Aim of the study: Understanding the role of TAMs and PD-1/PD-L1 networking in GC. Methods: A systematic review of published data was performed using MEDLINE (PubMed), Embase, and Cochrane databases. We retrieved articles investigating the co-existence of TAMs and PD-1 in GC and the prognosis of patients expressing high levels of PD-1+ TAMs. Results: Ten articles with a total of 2277 patients were included in the systematic review. The examined data suggest that the expression of PD-L1 has a positive correlation with the infiltration of TAMs and that patients who express high levels of PD-1+ TAMs may have a worse prognosis than those who express low levels of PD-1+ TAMs. Conclusions: TAMs play a pivotal role in the regulation of PD-1/PD-L1 networking and the progression of GC cells. Nevertheless, additional studies are needed to better define the role of TAMs and PD-1/PD-L1 networking in GC.