ALL subtype distinction based on discriminating genes identified by RMA/RF. Gene expression profiles from 104 paediatric ALL specimens were analyzed using unsupervised Principle Component Analysis (PCA). Shown are three-dimensional scatter plots of all cases using PCA with the top discriminating probe sets identified by RMA/RF. (A) Three-dimensional scatter plot of a PCA using the top 20 subgroup-discriminating probe sets (120 probe sets). (B) Three-dimensional scatter plot of a PCA using the top 5 subgroup-discriminating probe sets (30 probe sets). Arrows mark two BCR-ABL-expressing samples known to contain a BCR-ABL translocation and a hyperdiploid (>50 chromosomes) karyotype.