If the animal may be safely anesthetized, the best treatment is the surgical removal of the mammary gland and mass with or without the removal of associated lymph nodes. I was taught to always spay the dog at the same time to prevent further mammary tumors from developing. Now a days this is controversial. This still makes sense though, since spaying the animal at that time will prevent pyometra, hydrometra and other gynecological diseases from happening. While in the abdomen, it is a good idea to look at the liver lobes and any other organs for any metastatic activity. Some animals, at specialty practices, may receive radiation and other care. If infections are taken care of and seromas are prevented, most dogs and cats do fine post surgery.