The objective of this study was to identify novel pharmacogenetic determinants of treatment-related hepatotoxicity during the maintenance phase in children with acute lymphoblastic leukemia (ALL) or lymphoblastic lymphoma (LBL). Although the authors first determined whether genotypes of drug-metabolizing enzymes and transporters--glutathione S-transferase (GST) genes, GSTM1 positive/null, GSTT1 positive/null and GSTP1 A313G, methylenetetrahydrofolate reductase (MTHFR) C677T, reduced folate carrier 1 (RFC1) G80A, and breast cancer resistant protein (BCRP) C421A--were associated with hepatotoxicity for 24 patients, no significant difference was detected for genotype and allelic frequencies between the patients with and those without severe treatment-related hepatotoxicity. Therefore, the authors explored potential candidate polymorphisms associated with hepatotoxicity using the Illumina Infinium HumanHap300, encompassing more than 318,000 tag single-nucleotide polymorphisms (SNPs), for 8 of 24 patients with or without severe hepatotoxicity. Genome-wide genotyping uncovered a total of 28 candidate SNPs. rs1966862, in Rho GTPase-activating protein 24 (ARHGAP24), was the most significant of the candidates, and the genotypes of rs13424027 (PARD3B), rs1156304 (KCNIP4), rs10255262 (SLC13A1), rs7403531 (RASGRP1), and rs381423 (unidentified gene) were also significantly associated with severe hepatotoxicity. This study suggested rs1966862 (ARHGAP24) and the other SNPs to be predictive factors for drug-induced hepatotoxicity during the maintenance phase in pediatric patients with ALL or LBL.