Cumulative incidence curves for the risk of hematologic relapse for ALL patients assigned in the higher-risk arm of the Total XIIIB Protocol. Children with the GSTM1 nonnull genotype (n = 71) experienced a higher risk of relapse compared with children with the null genotype (n = 59) (P = .03) (A). Among patients with the GSTM1 nonnull genotype, those with the TYMS 3/3 genotype (n = 24) were at even higher risk of relapse compared with those with the TYMS 2/2 or 2/3 genotypes (n = 47) (P = .03) (B).