In a study of the tumor microenvironment (TME) of 2456 patients with GC, Chen et al. classified 4 subtypes—TMEclassifier-A, B, C, and D—and discovered that patients with the TMEclassifier-B subtype without chemotherapy benefit responded best to pembrolizumab treatment (PD-1 inhibitor). The gene discussed is PDCD1; the disease is neoplasm.