Moreover, in a cohort of 453 gastric cancer patients, high IL-9 expression was found to be associated with increased numbers and elevated killing activities of CD8+-infiltrating T lymphocytes (TILs), enhanced efficacy of anti-programmed cell death 1 (PD-1) immunotherapy based on the monoclonal antibody Pembrolizumab, and increased overall survival [22]. The gene discussed is PDCD1; the disease is gastric cancer.