Hierarchical clustering of human-dog combined dataset. Clustering of the combined gene expression data for 33 dog (17 malignant, 5 benign and 4 intermediate) and 129 human (68 malignant and 61 normal) breast samples. A subset of 600 most variable genes was selected (see Methods for details). Samples in each class (dog normal, benign, intermediate and malignant samples, and human normal and malignant samples) were hierarchically clustered separately based on the Pearson correlation coefficients, and then columns were ordered based on class membership. Genes were hierarchically clustered based on Pearson correlation coefficients. The histograms at the bottom represent for each sample (column) the respective signature score values [37–41] (see Methods).