Mammary Gland Tumors in Dogs
Dr. Jeffrey Philibert
Veterinary care should include diagnostic tests and subsequent treatment recommendations. Medical tests are needed to establish the diagnosis, exclude other diseases, and determine the impact of the mammary gland tumor on your dog. A complete medical history should be obtained and your veterinarian should complete a thorough physical examination.
Fine needle aspirate cytology of the tumor is a simple and safe technique in which a small needle is briefly inserted into the tumor mass to withdraw some cells. This sample is examined under a microscope by a pathologist. The results help to determine if the mass is a mammary gland tumor or some other form of cancer. Results from a fine needle aspirate test can be difficult to interpret. If the results indicate a malignant tumor, the tumor is removed. However, sometimes the cells appear benign yet the mass may still represent a malignant form of cancer. Thus, decisions to remove a mammary gland tumor surgically cannot be made solely on these results. Other factors, including the age, physical appearance, a more complete biopsy, or associated clinical findings, may determine the recommendation for surgery or not.
Chest X-rays allow your veterinarian to look for evidence of metastatic cancer that has spread. The lung is a frequent site of metastasis for this type of cancer.
Fine needle aspiration cytology of enlarged regional lymph nodes is appropriate. This test would help stage a cancer and provide a more accurate treatment plan and prognosis. This can be a very important test to decide if your dog needs to receive chemotherapy in addition to surgery.
Histopathology (biopsy) is done when the cause of a swelling is uncertain or whenever mammary gland tissue or adjacent lymph nodes are removed. The tissue is examined by a pathologist who determines the type of cancer, if the cells are benign or malignant, and if the cancer has been removed to the extent of the surgical margins. This information is crucial to your veterinarian for making recommendations about further therapy. Biopsy results may also determine if your dog should be evaluated by a veterinary oncologist, which is a specialist in the treatment of cancer.
Your veterinarian may recommend additional diagnostic tests to ensure optimal medical care. These are selected on a case-by-case basis.
A complete blood cell count (CBC) is a standard test to screen your pet's general health and to assure that it is safe to perform other procedures.
A blood biochemical profile is a simple blood test that helps to assess the general health of the body organs such as the liver and kidneys.
A urinalysis is often obtained to assess kidney function and the lower urinary tract for a hidden infection that might cause trouble if the immune system becomes suppressed.
Abdominal X-rays can be used to evaluate intra-abdominal organs such as the liver, internal lymph nodes, and visualize parts of the spine.
Abdominal ultrasound is a noninvasive study that permits visualization of soft tissue body organs such as the liver, kidneys, spleen, intestines, and lymph nodes. This test is often done to determine if the cancer has spread. There is no risk to your dog with this procedure, unless a biopsy procedure is also planned, in which case the risk is small. This test requires that the hair over the abdomen be clipped.
The treatment of cancer in dogs is almost identical to the treatment of cancer in people. Surgical removal of the cancer is the optimal treatment. A simple procedure called a lumpectomy suffices in some cases, while more radical mastectomy is required in others. If the type of cancer is confined to the mammary gland, mastectomy can be curative.
In the dog, the type of surgery does not seem to influence overall survival, so that less radical surgery – a simple mastectomy with removal of the adjacent glands – is often recommended
Any enlarged lymph nodes should be removed as well. If lymph nodes contain cancer cells, an oncologist should be consulted. Chemotherapy is generally necessary.
Because of the influence that hormones have on breast tumors, it is recommended that intact dogs be spayed at the time of surgery for the mammary gland tumor. Recent evidence suggests that removal of the ovaries may impact favorably on long term survival. Spaying can be performed at the same time as mastectomy.
Chemotherapy using drugs that kill cancer may be recommended in certain cases such as when the cancer has metastasized or it has a high potential to metastasize. Your veterinarian is likely to consult with you or refer you to a veterinary oncologist for this. There are many different types of chemotherapy drugs, including doxorubicin (Adriamycin), a commonly-used drug in mammary gland tumors.
Radiation therapy may be recommended to treat large tumors that are not amenable to surgical removal.
Anti-estrogen therapy with drugs like Tamoxifen, an anti-hormone agent used in women with breast cancer, has been used experimentally in dogs with mammary gland tumors. This therapy is rarely recommended in dogs as it does not seem as effective and can cause vaginal discharge, urinary incontinence (leaking urine), and pyometra (infection in the uterus).