Principal component analysis of human-dog combined dataset. Results of principal component analysis based on the subset of 9,963 human-dog orthologous genes. The 162 samples were projected on the first three principal components that capture ~44% of the total variability. Three main sample clusters are highlighted in colors. Cluster A contains the majority of human and dog tumors. Cluster B is a sub-cluster of cluster A and contains mostly 'benign' and 'intermediate' dog tumors. Cluster C includes almost all normal samples from human and dog. The genes contributing the most to the first principal component analysis were analyzed by genes set enrichment analysis and enriched gene sets (p < 0.05) were selected. Results are summarized along the grey arrow. Among the others, cell cycle (P = 6e-9) and DNA replication (P = 7e-6) emerged as enriched gene sets (up-regulated in both species tumors and listed on the right side of the arrow), as well as extracellular matrix (P = 0.0025), cell matrix adhesion (P = 0.0078), cell communication (P = 0.0207), TGF-β receptor signaling pathway (P = 0.0115) (down-regulated in both species tumors and listed on the left side of the arrow).