Are Canine Mammary Tumors Fatal?

Mammary tumors occur most frequently in unspayed female dogs and are extremely rare in male dogs. Mammary squamous carcinoma is also quite rare, presenting in less than 1 percent of primary invasive mammary gland carcinomas. If your pup has been diagnosed with this tumor, her prognosis depends on several factors.


Mammary Glands and Tumors

A dog's mammary glands run in two rows, extending from her chest to lower abdominal area. Their purpose is to produce milk to feed newborn pups, should your girl get pregnant. About half the dogs with mammary tumors have benign tumors, such as simple or complex adenomas. The remaining half of dogs with tumors have a variety of malignant mammary tumors, including fibrosarcomas and, very rarely, squamous carcinoma. Most mammary tumors appear in dogs 6 years old or older.

Symptoms and Diagnosis

Usually a painless lump or mass will present in the larger glands closest to a dog's rear. The size of the mass can vary from large to small and be clearly defined or indefinite. Some are stationary, clinging to muscle or skin, while others move freely. Sometimes a mass will bleed. The vet will take a blood sample for a complete blood count and chemical profile, and will conduct a urinalysis. A biopsy of the mass is necessary to determine potential malignancy, and X-rays help detect the extent of the tumor. The information gained from the exam will give the vet insight about a dog's prognosis.


Malignant tumors need to be removed, so surgery is the treatment of choice. A variety of influences determine how much tissue is removed during surgery. The dog's age, the type of tumor and rate of growth impact whether only the tumor is removed or if additional tissue from surrounding areas and lymph nodes is removed. In rare instances chemotherapy is added to the treatment regimen. During surgery, the vet will take a specimen for further examination to help determine the prognosis. Regular follow up examinations are necessary in one, three, six, nine and twelve months after the initial treatment to ensure there aren't more tumors or changes in the tissue.

Prognosis and Prevention

In malignant mammary tumors in dogs, carcinomas tend to have longer survival times than sarcomas. The tumor's size and grade, and whether lymph nodes are involved impact the chance of recovery. Generally, small tumors, less than an inch across, tend to have favorable cure rates. Larger, more aggressive tumors have a poorer prognosis. If you spot a lump in your pup's mammary gland, have your vet check it out immediately as these lumps can grow quickly if they're malignant. Early detection makes recovery more likely.

By Betty Lewis

About the Author
Betty Lewis has been writing professionally since 2000, specializing in animal care and issues, business analysis and homeland security. Lewis holds a bachelor's degree in journalism from West Virginia University as well as master's degrees from Old Dominion University and Tulane University.