CD38 and neoplasm: The key steps of this pathway are: 1) the activation of intracellular CD38 by protein kinase A following the interaction of the NK cell with a tumor cell results in the production of ADPR, 2) ADPR targets TRPM2 channels on cytolytic granules, and 3) TRPM2-mediated Ca2+ signaling induces cytolytic granule polarization and degranulation, resulting in antitumor activity.