The National Comprehensive Cancer Network (NCCN) guidelines for the treatment of gastric cancer recommend that PD-L1 testing should be considered for patients with a definite diagnosis or suspected locally advanced, recurrent, or metastatic gastric adenocarcinoma who are proposed for immunotherapy. The purpose of PD-L1 testing is to enable physicians to develop more targeted, individualized regimens. Currently, immunohistochemistry is the main method used in clinical practice for PD-L1 testing, and the results are given by the pathologist under the microscope after obtaining the specimen tissue.
Why test for PD-L1? PD-L1 is a ligand for programmed cell death-1 (PD-1), which is involved in tumor immune escape, meaning that PD-L1 expressed on the surface of tumor cells can bind to PD-1 on the surface of the body’s T lymphocytes, which are responsible for killing tumors, thereby inhibiting the action of T lymphocytes and allowing tumor cells to escape from T lymphocytes. tumor cells to escape from the killing of T lymphocytes. About 24% to 42% of gastric cancers express PD-L1, and for PD-L1-positive gastric adenocarcinoma, physicians may consider immunologic drugs such as pembrolizumab as third-line or follow-up treatment. 53% of patients with PD-L1-positive advanced gastric cancer showed tumor regression with pembrolizumab. (Siwei Pan, Department of Gastrointestinal Oncology, The First Hospital of China Medical University, contributed to the answer)