“…The folate analog methotrexate (MTX) and the thio-substituted purine analog 6-mercaptopurine (6MP) became pioneering anticancer agents more than half a century ago, when first Farber et al1 and then Burchenal2,3 demonstrated that such drugs can induce temporary remissions in childhood leukemia. Soon cure became the goal,4,5 and through a series of trials it was shown that the chance of long-term remission of childhood acute lymphoblastic leukemia (ALL) was significantly improved, when patients received several years of postremission maintenance therapy with daily 6MP and weekly MTX 4–8.…”