Most veterinarians will take a thorough history from any dog’s owner about its overall health, and also perform a complete nose-to-tail physical examination, regardless of why the animal has been brought to the clinic. Sometimes, breast tumors are detected incidentally during a routine annual physical examination, while other times the owner brings her pet to the doctor specifically because she has felt something lumpy in one or more of her dog’s mammary glands. In either case, once a mammary mass is identified, the veterinarian probably will recommend drawing blood and urine samples and submitting them for analysis. While the results of these tests can’t identify breast cancer or the type of tumor per se, they are helpful to detect other medical abnormalities that may affect the dog’s overall health. The veterinarian may measure the size of each tumor and assess whether it is “fixed” or “floating” inside the mammary gland. Often, a chart is made of the location, size and nature of each mass and put into the dog’s medical file so that any subsequent changes can be easily chronicled. The doctor will palpate the dog’s peripheral lymph nodes, to see whether they are enlarged (which could indicate metastasis of the tumors).
Breast cancer is by far the most likely cause of any mass in the mammary gland(s) of an older female dog. The most definitive way to diagnose breast cancer is to remove the tumor surgically (called an “excisional biopsy”) and send the tissue to a special laboratory for microscopic evaluation called “histopathology”. Other techniques, such as taking aspirates from masses through sterile needles (fine needle aspiration) or taking incisional biopsies (where only punches or parts of the tumors are removed) are inconclusive, because they only permit evaluation of certain cells that may not represent the entire tumor and may mimic malignant cancer but actually reflect simple inflammation.
Many times, even before a histological confirmation of breast cancer is made, the doctor will advise taking a series of radiographs (X-rays) to “look around” and see whether there is evidence of spread to remote places. Abdominal (belly) X-rays can reveal metastasis to nearby lymph nodes, and thoracic (chest) X-rays can disclose metastasis to the lungs. Ultrasonography can also be used to look for spread to abdominal organs or lymph nodes. More advance radiological techniques, such as computed tomography (CT scan) and magnetic resonance imaging (MRI), are more sensitive for the detection of tumor metastasis to the chest and/or lungs, but are not available everywhere and are much more expensive to perform than standard X-rays. Once cancer has spread widely, it probably doesn’t matter what exact type of cancer cell is involved. The prognosis for dogs with cancer that has metastasized throughout its body is guarded to grave.
Breast cancer isn’t all that difficult to diagnose, once mammary masses are identified. The quickest way to diagnose this disease is to remove one or more of the masses and have it evaluated. Radiological evidence of metastasis strongly suggests that the tumors (or tumors somewhere in the dog’s body) are malignant and may make specific identification of the cancer type a moot point.