Analysis flowchart: overview of the strategy used for gene selection using Set-A microarray data. At each level, the data set was filtered to remove genes that showed poor robustness and no significant difference in expression level between the TEL/AML1-positive and the TEL/AML1-negative ALL subclasses. SAM denotes Significant Analysis of Microarrays. Two groups of genes (according to the filters applied) were selected and functionally annotated. Nine of the 16 genes were selected for RT-PCR validation on the basis of their biological relevance.