HCAR1 and neoplasm: In cancer cells the production of lactate and H+ ions plays crucial roles in: (i) synthesis of NAD+ necessary to sustain the increased rate of glycolysis; (ii) acidification of the tumour microenvironment, thus reducing the viability of normal cells and favouring the infiltration of neoplastic cells [134]; and (iii) binding to specific receptors on target cells, such as GPR81, thus activating intracellular signalling cascades, lactate uptake, mitochondrial metabolism, angiogenesis and tumour growth [135–137].