The type of surgery depends on the size, location, and number of mammary tumors and species of your pet. In general, surgery is more conservative for dogs with mammary tumors and involves removal of either the mass alone or the affected mammary gland. However, in cats, more aggressive surgery is recommended with removal of one or preferably both sets of mammary glands (Figure 3). Surgery to remove both sets of mammary glands from a cat is often done in two surgical procedures 2–3 weeks apart.
The local lymph node should also be removed in cats, if possible, to assess for evidence of spread of the cancer.
The role of spaying female dogs with mammary tumors is controversial. Most studies have shown no beneficial effect of spaying at the time of tumor removal in preventing the development of new mammary tumors or influencing the aggressiveness or metastatic potential of existing mammary tumors. However spaying at the time of mammary tumor resection may be recommended by your veterinary surgeon because recent studies have shown a beneficial effect in dogs with mammary tumors and it can prevent unrelated diseases, such as pyometra (uterine infection).
The role of chemotherapy in cats and dogs with malignant mammary tumors has not been clearly defined for all tumor types but oncologist consultation after surgery is often recommended. For most mammary tumors in cats and dogs, hormonal therapy, immunotherapy, and radiation therapy have either not been investigated or are not beneficial.