Just skimmed the article, and it seems to me that they are more looking into this to find a treatment for brain cancer than making a direct causality from the supplement itself. Basically when someone does have brain cancer, they could limit NAMPT to help in treatment. That's how I read it at least, maybe I'm misinterpreting. There is these quote:
“We didn’t directly demonstrate that taking NAD+ precursors makes tumors grow faster, but one implication of our work is that if you want to take anti-aging NAD+ precursors, you might want to keep in mind that we don’t yet understand all the risks.”
"Furthermore, the scientists found that glioblastoma cells responded to radiation therapy – a standard therapy used to treat the disease in people – by increasing expression of NAD+ pathway genes, and that inhibiting NAMPT before dosing the cells with radiation made them easier to kill."
“We didn’t directly demonstrate that taking NAD+ precursors makes tumors grow faster, but one implication of our work is that if you want to take anti-aging NAD+ precursors, you might want to keep in mind that we don’t yet understand all the risks.”
"Furthermore, the scientists found that glioblastoma cells responded to radiation therapy – a standard therapy used to treat the disease in people – by increasing expression of NAD+ pathway genes, and that inhibiting NAMPT before dosing the cells with radiation made them easier to kill."