Cluster dendrogram of 16 MRD-HR and 22 MRD-SR specimens. Hierarchical clustering analysis was carried out considering only those clones that had a 4-fold difference in expression from the mean on at least 2 arrays (1579 clones). Each column represents 1 sample. (▪) MRD-HR samples. (□) MRD-SR samples. The cluster of 4 samples with an E2A-PBX1 rearrangement is indicated.