Mammary tumors are most frequent in intact female dogs, and extremely rare in male dogs. Most often, the two posterior mammary glands are involved than the three anterior glands. These tumors appear as single or multiple modules (1-25cm) in one or more glands. The surface of the nodule is usually lobulated, grey in color, firm, and sometimes with cysts filled with fluid. There can be mixed mammary tumors that can contain cartilage or bone on the cut surface.
Ovariectomy generally decreases the risk of developing mammary neoplasia. Spaying before the first estrus lowers the risk of mammary tumors to 0.5%, and after the first estrus to 8%. Female dogs that are spayed after maturity are considered at the same level of risk of developing mammary tumors as intact female dogs.
The most common indication of a mammary tumor is a palpable mass under the skin in the mammary area. Other signs may include discharge from the mammary gland, ulceration of the skin over the gland, swelling of the mammary gland and pain, inappetence, loss of weight and weakness.
Mammary tumors are almost always treated surgically. Options are the following: lumpectomy (removal only of the tumor), simple mastectomy (removal only of the affected gland), modified radical mastectomy (removal of the tumorous gland along with the glands that share the same lymphatic drainage and the associated lymph nodes), and radical mastectomy (removal of the whole mammary chain along with the associated lymph nodes).
Till now, chemotherapy has not shown as an effective treatment for mammary tumors in dogs.
In the video below you can see some examples of mammary tumors in dogs that were published on our Facebook page.
If you would like to know more about reproductive tumors, read “Tumors of the reproductive system in female dogs” on our blog.