HCAR2 and neoplasm: G protein-coupled receptor ligands, that are encoded by the microbiota and are agonists to receptors (e.g. SCFAs) that have important implications for gastrointestinal and metabolic physiology, has been shown to function as a tumor suppressor in the colon (e.g. GPR109A) (Cani and Jordan, 2018; Lavelle and Sokoi, 2020).