Cancer. The Big C. It can be a scary word when thought of in conjunction with family, friends, and pets. Breast (or mammary) cancer can also be seen in pets, and in some cases, it can be deadly as well.
Cancer occurs because of genetic damage to cells which cause mutations in the DNA of the cell. More mutations can occur while an animal ages, leading to cancer. Additionally, there may be a genetic predisposition for some cancers. Mammary cancer is a tumor originating from mammary or breast tissue. These masses can be completely benign, locally invasive (invade surrounding tissues), or metastatic (spread to other parts of the body). Some of these masses can be cured by surgical removal, but some will reoccur or necessitate additional therapy.
Mammary cancers in humans tend to occur most frequently in female dogs who are typically around 10 years of age. In pets, they are more common in intact (non-spayed) females. Sex hormones seem to be the most important factor in the development of mammary tumors in dogs. Early spaying can dramatically reduce the risk of mammary cancer. If spaying occurs prior to first heat, there is basically no risk of mammary neoplasia. If spaying is done after the first heat cycle, the risk of breast cancer increases to 8 %. If spaying is delayed until after the second heat cycle, there is a 26% chance of developing breast cancer. After the dog has had three or more heat cycles, there is no sparing effect on the risk of developing breast or mammary tumors.
Additionally, it has been recently shown that dogs that are overweight at a young age have a higher risk of developing breast tumors as they age. If a dog is thin at a young age, it can decrease the risk of some mammary cancers by 40%. If a male dog is affected with breast cancer, the prognosis is usually grave.
Mammary masses can appear in one or more glands. They tend to occur in the last two sets of glands (near the hind legs). They can be firm, soft, ulcerated, freely movable, adhered to other tissue, well defined, or diffusely swollen. They can vary in size and may grow slowly or quickly. It is difficult to distinguish between a malignant and benign mass on palpation and exam alone. Signs can vary, and many dogs exhibit no signs, even if the mass is malignant. In some cases, there may be discharge from the mammary gland, ulceration over the mass, pain, anorexia, weight loss, lethargy, and weakness.
If a mass is noted in the mammary gland (or anywhere else), we recommend an evaluation as soon as possible. At your visit, we may recommend some diagnostics like a fine needle biopsy. This is done with a small needle that is placed into the mass. When the needle is removed, there will be cells on the needle that may allow us to distinguish if this is a mass we should be concerned about. Additionally, other diagnostics may be of value like blood work (complete blood count, blood chemistry/organ function, and thyroid levels), a urinalysis, or a fecal sample. Radiographs (x-rays) of the chest/abdomen may also be done to look for evidence of metastasis.
In many cases (even if the tumor is malignant) surgery can be curative, but a biopsy must be done on the removed tissue to confirm if removal is curative or not. Chemotherapy, if needed, can be performed if needed. If the patient is still un-spayed, it is typically recommended to spay at the time of the mass removal because it can decrease the possibility of recurrence.
Approximately 50% of all mammary masses are malignant. Surgery can be curative for a lot of cases, even if malignancy is present. The prognosis for dogs with malignant mammary tumors depends on the following factors: tumor type, size, regional lymph node (lymph gland) involvement, presence or absence of distant metastases, completeness of resection, local behavior, rapid growth, ulceration, attachment to other tissues, vascular or lymphatic invasion, and tumor differentiation.
After removal, we recommend annual physical exams and preventative care as recommended by our veterinary staff. Radiographs may be recommended periodically if the mass was malignant or not completely resected to monitor for metastasis.
Owners should examine their dogs at regular intervals for any lumps, bumps, or swellings and take them for yearly veterinary checkups. All lumps should be surgically removed and biopsied. Early diagnosis and treatment are crucial for a good outcome.
-Kelvin Urday D.V.M.
-Kelvin Urday D.V.M.