Mammary Gland Carcinoma in Dogs
What is Mammary Gland Carcinoma?
In dogs, approximately half 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
Treatment of mammary tumors is aimed both at 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 (lumpectomy/reasonably wide excision vs. radical mastectomy) is debatable. In general, the recommendation is to remove sufficient tissue to ensure adequately wide and histologically clean margins. In addition to surgery and depending on identification of various prognostic factors identified below, adjuvant systemic chemotherapy can be considered in an effort to delay or prevent metastasis. Based on somewhat limited reports in the literature and responses in other types of carcinomas, two drugs could be considered: doxorubicin or a platinum drug (carboplatin or cisplatin) given at 3-week intervals for a total of four-six 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, and 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 you should 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.
Various prognostic factors for canine mammary tumors have been identified including:
- Tumor size: In one study, dogs with tumors >5cm in diameter had a median survival time of 40 weeks compared to 112 weeks for animals with smaller tumors following surgery.
- Histologic grade: In one study where histologic grade was adopted from a human pathologic staging system, carcinomas were divided into 4 categories. In that study, only 19% of the dogs with grade 0 (in situ or non-invasive) carcinomas had recurrence or metastasis in 2 years, compared with 60% of dogs with grade I (stromal invasion) carcinomas and 97% of dogs with grade II (angiolymphatic invasion) carcinomas. A grading scheme based on nuclear differentiation has also been reported in which dogs with poorly differentiated tumors had an increased risk of developing recurrent or metastatic carcinoma within 2 years of surgery, with an overall rate of 90% compared to 68% and 24% for dogs with moderately- or well-differentiated carcinomas, respectively. (We recommend contacting the pathologist for this information on Oreo).
- Lymph node metastasis
- Lymphoid cellular activity: Lymphocyte infiltration may indicate an antitumor response and is associated with a more favorable prognosis.
- Bostock DE . Canine and feline mammary neoplasms. Br Vet J 1986;142:506-515.
- Gilbertson SR, Kurzman ID, Zachrau RE, et al. Canine mammary epithelial neoplasms: Biological implications of morphologic characteristics assessed in 232 dogs. Vet Pathol 1983;20:127-142.