Canine Mammary Adenocarcinoma

When grooming your dog, always feel her stomach to check for lumps.
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Canine mammary adenocarcinoma is a type canine breast cancer that develops in the epithelium, or area of the breast that produces milk. While only 45 percent of all mammary tumors are malignant, adenocarcinoma is a malignant variety. However, this is one form of canine cancer where you can play a role in your dog’s risk factor.


Similar to humans, mammary adenocarcinoma and other mammary tumors present as lumps in the mammary tissue. Benign tumors are often small and slow-growing while malignant tumors tend to be larger with rapid growth. Malignant tumors are often irregular in shape. While female dogs have eight to ten mammary glands, tumors most often present in the glands closest to the hind legs. If you notice lumps, consult a veterinarian immediately. In later stages of cancer, weight loss is also common. If the cancer has spread into the lungs, your dog may experience shortness of breath or difficulty breathing.

Risk Factors

Unspayed female dogs between the ages of 5 and 10 are at the greatest risk of developing mammary adenocarcinoma. In addition, Brittany spaniels, cocker spaniels, English springer spaniels, English setters, German shepherds, Maltese, pointers, poodles and Yorkshire terriers are at an increased genetic risk.


Treatment of mammary tumors, regardless of being benign or malignant, is surgical removal. After a thorough examination, your veterinarian will remove the tumor alone or choose to remove the surrounding tissue, lymph nodes and mammary glands. If the entire tumor is unable to be removed, chemotherapy may be recommended, although this is uncommon. Regular checkups are necessary as are regular exams to look for signs of new tumors.

Risk Reduction

Mammary tumors are more common in unsprayed female dogs, with a risk as high as 26 percent. However, spaying your female dog before her first estrous cycle greatly reduces the risk of developing mammary tumors. If spaying before the first heat is not an option, spaying before the age of 2 1/2 still reduces the risk. Unfortunately, after that age, spaying will no longer lower the risk of tumor development. If you do not plan to breed your dog, early spaying is the best way to reduce this cancer risk.