PIK3CA and mucosal melanoma: We observed numerous dog–human homologies, including significant mutation of the same residues (e.g., PIK3CA H1047 is mutated in >25% of mammary tumors of both species) and genes (e.g., in both species, TP53 is mutated in >25% osteosarcomas and MDM2 is amplified in about 40% oral or mucosal melanomas) (Fig. 4).