SIRT1 and neoplasm: The other NAD+-consuming enzymes, the SIRTs, are also up-regulated in a range of cancer types, as they are also used by tumours to promote their cell proliferation and progression through mechanisms involving NMPRT regulation of SIRT1 activity and a positive feedback loop of c-Myc-NMPRT-SIRT1 ([68] and references cited therein).