HCAR1 and breast cancer: In non-cancer human breast epithelial cells (MCF10A) and in triple-negative (MDA-MB-231) breast cancer cells, GPR81 mRNA expression was higher in lactate-rich medium (20 mM lactate, 0 mM glucose) than in normal glucose (5 mM) medium, after 72 h (Fig. 2a-b), confirming earlier findings in pancreatic [18] and lung [37] cancer cells.