Increased hypoxanthine (HX) competitively inhibits activation of 6‐MP and 6‐TG, leading to thiopurine resistance and tumor relapse.5 In addition to 6‐MP and 6‐TG, PRPS1 mutant cells also confer slight resistance to other commonly used ALL chemotherapeutic drugs, such as methotrexate (MTX) and cytosine arabinoside (Ara‐C). This evidence concerns the gene PRPS1 and acute lymphoblastic leukemia.