TPMT and cancer: A subsequent NOPHO trial (NOPHO ALL‐2000) reported that using reduced mercaptopurine dosages for the TPMT heterozygote patient, alongside high‐dose methotrexate, reduced the risk of developing second cancers but this was counterbalanced by an increased risk of relapse for the TPMT heterozygote (Levinsen et al, 2014).