CD38 and neoplasm: Acting as a metabolic sensor in both normal and tumor cells, at physiological pH CD38 catalyzes the transformation of extracellular β-NAD+ (NAD+-glycohydrolase activity) to produce ~2% of Cyclic ADP Ribose (cADPR) (cycling activity) and ~90% of ADPR (hydrolytic activity), simultaneously releasing nicotinamide (Nam) [27].