For example, among the hot metabolites, i.e., metabolites that are enriched in tumors with dense CD8+ TILs, linoleate and the microbiota-derived 3-formylindole (also called indole-3-aldehyde) were reported to stimulate cytotoxic T cell (CTL)-dependent anti-tumor immunity (Fig. 2d).(38, 39) Hot metabolites also include salicylate and 2-hydroxyhippurate (salicylurate), both of which are metabolic derivatives of aspirin (acetylsalicylic acid). This evidence concerns the gene CD8A and neoplasm.