ABCC2 and acute lymphoblastic leukemia: Conversely, Lopez-Lopez et al, in a cohort of 151 children with ALL, suggested that the ABCC2 rs3740065 G allele was significantly associated with high MTX concentration at 72 hours and an elevated risk of MTX-related toxicity.20 Although no genetic variant of ABCC2 rs2273697 was found to have an impact on serum MTX concentration and MTX elimination delay as previously reported,23,28 patients with the ABCC2 rs2273697 A allele had a higher risk of developing hepatoxicity (increased AST).