The dog has often served as a model animal for humans in scientific studies. This is due to the fact that dogs are susceptible to a wide range of diseases which also affect humans. One example is cancer, a condition that affects dogs as well as owners. Neoplastic diseases account for 18-23 % of all deaths in dogs (Bonnet et al., 2005 and Jagielski et al., 2002). Mammary tumor, or tumor of the breast, is the most common tumor form in intact dogs and women (Im et al., 2013). Mammary tumors originate in the udder, and are classified according to their histological characteristics.