Hierarchical clustering of gene-expression data. Measurements of gene expression from 122 microarray analyses of the 101 nonfollicular small B-cell lymphoma samples of the preliminary group, and the 2 mantle cell lines (NCEB; GRANTA) are depicted. Each column represents the genomic profile of the 2533 expressed genes for one tumor, and each row represents the relative level of expression of one cDNA clone. Red indicates a high level of expression of messenger RNA of the given gene in the tumor, as compared with the median value of this gene, and green indicates a low level of expression, according to the color scale. Gray indicates missing data. Correlated genes are grouped across the samples into clusters localized by the colored boxes. The dendrogram, reported also at the top of the hierarchical clustering, lists the samples studied and provides a measure of the relatedness of gene expression in each sample. SLL cases are colored in orange, MZL cases in blue, MCL cases in pink, and cases reclassified as borderline cases in brown. The dots at the right side of the hierarchical clustering represent the genes that significantly discriminate the 3 entities. The orange dots represent the genes that discriminated the SLL entity, the blue dots the MZL entity, and the pink dots the MCL entity.