I have never owned a dog, but found this interesting. Some recent Brazilian research suggests that her2+++ mammary cancer occurs in dogs: A.P. Dutra1, N.V.M. Granja2, F.C. Schmitt3 and G.D. Cassali1
c-erbB-2 expression and nuclear pleomorphism in canine mammary tumors http://www.scielo.br/scielo.php?scri...lng=en&nrm=iso
although one Japanese study (Immunohistochemical analysis of c-yes and c-erbB-2 oncogene products and p53 tumor suppressor protein in canine mammary tumors) found no connection.
A Spanish study found that her2 overexpression, not overamplification occurred in dogs:
http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_docsum
but a Japanese study did not find her2 expression to be common in dog cancer.
The oldest study, based in the U.S. (Expression of the oncogene c-erbB-2 in canine mammary cancers and tumor-derived cell lines), found a very high rate of her2+++ among dogs.
However, viruses like MMTV are known to be more common in some areas than others, so regional variations migh help to explain the wide range of findings.