Hierarchical clustering of Affymetrix and spotted cDNA expression profiles of 60 cell lines. Dendrograms showings average linkage hierarchical clustering of NCI60 human cancer cell lines using Spearman Rank correlations. Cluster analyses of the 60 cell lines based on A) gene expression profiles of 1415 genes from the Ross spotted cDNA array dataset and B) 1517 genes from the Staunton Affymetrix dataset are shown. The cell lines are coloured as in Figure 1. The colon tumour cell line HT29 and cluster of colon tumour cell lines are highlighted by a green arrow and bar respectively.