According to several studies, MTAP-negative tumor cells are up to 20 times more susceptible to purine biosynthesis inhibitors such as MTX, 6-mercaptopurine, azaserine (a powerful inhibitor of the first step in purine biosynthesis), and L-alanosine, than MTAP-positive cells are [50, 55, 56]. Here, MTAP is linked to neoplasm.