Figure 4. Comparison of the gene expression patterns in clinical breast cancer specimens and cultured breast cancer and leukemia cell lines. (A) Two-dimensional hierarchical clustering applied to gene expression data for two breast cancer specimens, a lymph node metastasis from one patient, normal breast, NCI60 breast and leukemia cell lines. The gene expression data from tissue specimens was clustered along with expression data from a subset of the NCI60 cell-lines, to explore whether features of expression patterns observed in specific cell lines could be identified in the tissue samples. Labels indicate gene clusters, shown in detail in Figure 5, that could be related to specific cellular components of the tumor specimens (see text). (B) Breast cancer specimen stained with anti-keratin antibodies. The arrows point to different cell types in this histologically complex tissue that could be distinguished by the cluster analysis.