Dendrogram of cluster analysis. Fifty-six CLL samples from fludarabine-naive patients were analyzed for gene expression of 7 genes involved in fludarabine transport and metabolism. Uncentered hierarchical gene clustering analysis organized the samples displayed graphically in the form of a dendrogram. Samples with similar expression patterns of the 7 genes are adjacent to one another, and the dendrogram branch lengths reflect the degree of similarity between the clustered groups. Two major expression patterns (cluster 1 and cluster 2) are identified.