Feline mammary gland tumors are the 3rd most common feline tumor and are most commonly diagnosed in middle aged to older cats. Incidence of mammary tumors is dependent on when cats are spayed. Cats who are spayed prior to 6 months of age have a 91% reduced risk of developing mammary cancer. Spaying after 2 years does not decrease the risk for developing mammary tumors.
Unfortunately, the majority (80-90%) of mammary gland tumors in cats are malignant, and 80-90% will metastasize (spread to other areas of the body) during the course of disease. The most common sites of metastasis include the regional lymph nodes and lungs. Due to the risk for metastasis associated with mammary tumors, thorough staging is recommended prior to any definitive treatment. This would include bloodwork (complete blood count and chemistry panel), urinalysis, aspiration of the regional lymph nodes, chest radiographs and an abdominal ultrasound. Prognosis for patients is dependent on the stage of disease. Stage is based on the size of the tumor (tumors less than 2cm have a better prognosis) and evidence of metastasis (patients that have metastasis typically experience a shorter survival time than those without). Another important factor is whether there is any evidence of invasion into the blood vessels or lymphatics which is determined from the biopsy (cats that do not have any invasion have a better prognosis than those that do).
|STAGE||T Size of Tumor||N Lymph Node Metastasis||M Distant Metastasis|
|Stage IV||Any size||Yes||Yes|
Treatment options include surgery, chemotherapy and supportive care. When possible, surgery is the recommended first step. Local tumor recurrence is common if the tumor is incomplete or narrowly excised, so wide surgical margins (2-3cms and one tissue plane deep) are recommended. This may mean that several mammary glands are removed at one time (known as a chain mastectomy).
Since most of these tumors will metastasize, chemotherapy may be discussed to address the risk of the tumor spreading. The most commonly used chemotherapy agents include doxorubicin (Adriamycin) and carboplatin. Both of these chemotherapy agents are administered intravenously once every three weeks for a total of four to six treatments when combined with surgery. In some situations, chemotherapy may be used without surgery, but the long term prognosis is not as good when surgery is not performed. Side effects of chemotherapy are typically mild and resolve on their own within 1-2 days. Chemotherapy side effects may include lethargy, poor appetite/anorexia, nausea, vomiting, diarrhea, and a decreased white blood cell count. Doxorubicin can also cause dose cumulative damage to the kidneys, so bloodwork is performed at each visit to ensure that it is safe to continue with chemotherapy.
Supportive care may include pain medications, anti-inflammatories and antibiotics as needed. This can be used with or without other treatment options.
Mammary gland cancer is not usually a cancer that is curable, but with treatment, can be controlled while maintaining your pet’s good quality of life. Your oncologist will be able to discuss the treatment options, prognosis and help guide you as to the most appropriate plan for your beloved family member.