GSTM1 and acute lymphoblastic leukemia: Our findings regarding GSTM1 and GSTT1 deletion polymorphisms are most closely consistent with those reported by Kim et al. In their investigation of the pharmacogenetic impact of MTX resistance and toxicity in patients with ALL, the authors did not identify any link between GSTM1 and GSTT1 deletion polymorphisms and MTX toxicity or resistance, despite GSTs being implicated in MTX metabolism.