Expression levels (natural log-scaled signal intensities) of GSTM1, based on GSTM1 genotype among patients in the higher-risk arm, and of TYMS, based on TYMS genotype, among those with GSTM1 nonnull genotype. The boxes and central horizontal define the quartiles and median; the whiskers represent the 10th and 90th percentiles. The number of patients (n) included in each group is indicated below the plots.