Relation between MTX-PG concentrations in ALL blasts and chromosome 21 copy number. (A) Data for B-lineage ALL blasts isolated from bone marrow at 44 hours after low-dose MTX treatment of 60 children (n = 43, 7, and 10 for 2, 3, and 4 copies of chromosome 21, respectively). (B) Data for B-lineage ALL blasts isolated from 61 patients at 44 hours after treatment with high-dose MTX (n = 42, 10, and 9 for 2, 3, and 4 copies of chromosome 21, respectively). (▪) Mean values; the boxes depict the standard errors (SE) of the mean; and the bars depict the range of ±1 standard deviation (SD) in each group. The SE and SD are symmetrical because they were calculated from log-transformed values of log-normal data.