Mammary Gland Carcinoma in Cats
What is Mammary Gland Carcinoma?
In cats, approximately 80-90% of all mammary tumors are malignant. Mammary carcinoma is locally invasive, extending into underlying normal tissues, and has the potential to spread to other places in the body (called metastasis).
Diagnostic tests are recommended to determine which sites in the body are involved. These tests include:
- Complete blood count (CBC)
- Serum biochemistry panel
- Urinalysis (U/A)
- Regional lymph node evaluation
- Thoracic radiographs
- Abdominal sonogram
Tumor size has been shown to be an important prognostic factor. Cats with tumors >3cm have a reported median survival of 6 months, cats with tumors 2-3cm in diameter have a median survival of 2 years, and cats with tumors <2cm have a median survival of approximately 3 years following surgery. Tumor histologic grade has also been shown to be an important prognostic factor.
Treatment of mammary tumors is aimed at both local control (removing the primary tumor and minimizing the likelihood of local recurrence) and systemic control (delaying or preventing metastatic disease). The surgery of choice is a radical mastectomy, since this type of surgery significantly reduces the chance of local recurrence. In addition to surgery, we recommend systemic chemotherapy to delay or prevent metastatic disease. Two drugs could be considered: adriamycin (either alone or in combination with cytoxan) or carboplatin, given at 3-week intervals for a total of 4-6 treatments. Chemotherapy drugs work by targeting fast-growing cells; cancer cells divide faster and abnormally compared to normal cells. Because of this, chemotherapy preferentially destroys cancer and spares normal tissues. There is the potential for some normal tissues with rapid growth rates (intestinal lining, bone marrow, hair cells) to be transiently damaged by chemotherapy. However, our goal in treating cancer in animals is quality of life, so the dosages are lower than those used in people. We do not normally see significant toxicity with chemotherapy. There is always some risk when a drug is given for the first time, and the oncologist will discuss what types of side effects may develop and what to watch for. If the pet has no problems the first time they receive a drug, they should have no problems with subsequent treatments of that drug. If the pet experiences any side effects, we address them as needed and lower the dosage of the causative drug for future treatments to prevent recurrent problems.
Another medication to consider is piroxicam. This oral Non-Steroidal Anti-Inflammatory Drug (NSAID) has anti-inflammatory and analgesic properties as well as possible anti-tumor activity against carcinomas. This medication should be given with food and the pet owner instructed to watch for signs of gastrointestinal upset (vomiting, change in stool, etc.). If such signs develop, piroxicam should be discontinued for 3-5 days. Restarting of therapy can then be considered in conjunction with the stomach-protectant misoprostil.
- MacEwen EG, Hayes AA, Harvey HJ, et al. Prognostic factors for feline mammary tumors. J Am Vet Med Assoc 1984;185:201-204.
- Castagnaro M, Casalone C, Bozzetta E, et al. Tumour grading and the one-year post-surgical prognosis in feline mammary carcinomas. J Comp Path 1998;119:263-275.