Classification and regression tree based on all 213 patients with cytogenetically determined chromosome copy number for predictors of MTXPG accumulation. ALL subtype was the strongest predictor of MTXPG accumulation (P = 8.71 × 10−5), followed by chromosome 18 copy number (chr18cnv) (P = 1.6 × 10−5; adjusted for subtype), and chromosome 10 copy number (chr10cnv) in patients with no chromosome 18 gain (P = .192; adjusted for subtype). Numbers in circles indicate the mean MTXPG concentration in patient leukemia cells (pmol/109 cells), also depicted in the bar chart below.