Calcium 2-hydroxypropanoate (pentahydrate) acts as an activator of the hydroxyl-carboxylic acid receptor 1 (HCAR1) and serves as an epigenetic regulator that induces lysine residue lactylation. This compound, a glycolysis end product, bridges the gap between glycolysis and oxidative phosphorylation and functions as a tumor metabolite with immunoprotective effects of lactate in antitumor immunity.