Benign and malignant tumors of mammary glands occur, usually in non-spayed female dogs. Spaying can largely reduce the risk of development of this cancer.

Mammary gland tumors in dogs

Mammary glands are located in two rows that extend from the chest to the lower abdominal area. The function of the mammary gland is to produce milk to feed newborn puppies. Basically, there are two main types of mammary gland breast tumors. Causes of the tumor may be hormonal or genetical.

Many genes are identified in dogs that are predisposed to cancer of the mammary glands. Genetic cause is a possible reason in many breeds like pointers, German shepherd, Maltese, and Yorkshire terriers, miniature poodles, English springer spaniels, cocker spaniels and English setters. These breeds are more prone to have breast or mammary tumor development as compared to other breeds.

The tumor is less common in dogs younger than five years of age. In female dogs, 50% of mammary carcinomas are benign and 50% are malignant. However, some of the malignant mammary tumors are fatal. About half of affected dogs will be diagnosed with the benign form of mammary tumors, which may be classified as complex adenomas, simple adenomas, fibroadenomas and duct papilloma.


A good general physical examination is needed to find the location, size, and character of all the mammary masses and analyze local lymph node enlargement. Following parameters help in diagnosis of tumors.

  • Complete blood count: blood count, chemistry, urinalysis, and clotting profile
  • Abdominal ultrasound, chest x-rays and CT scan are used to check for cancer that has spread to other parts of the body.
  • Aspiration (Fine Needle Aspiration): a needle is used to sample the mammary mass to help distinguish it from other skin tumors. Lymph nodes also assessed to look for a spread of cancerous cells. This is more reliable in dogs than cats to confirm a diagnosis.
  • A biopsy may be indicated to rule out certain kinds of tumor known as inflammatory mammary carcinoma, as surgery is generally not recommended for such tumor type.


A palpable mass underneath the skin of the abdomen is the most common findings in dogs with mammary tumors. However, other signs and symptoms include discharge from a mammary gland, ulceration of the skin over a gland, painful, swollen breasts, loss of appetite, weight loss, and generalized weakness. For most mammary tumors, surgical removal is recommended.

Tumor depend upon the age of your dog, and the rate at which tumor metastasized. Surgery is the primary mode of treatment. Remove only tumorous part or remove all of the tumor along with the surrounding tissue, lymph nodes and mammary glands.

Sometimes, chemotherapy is required following surgery. The prognosis is good after surgical resection for most mammary tumors in female dogs, but for certain types of tumor, prognosis is worse.

Some types of tumor are more invasive, rotting deeper into the tissue or bone makes them very difficult to remove. In such cases, partial removal of the cancerous mass and surrounding tissue is performed and chemotherapy is also an option, but use of chemotherapy for breast or mammary tumors is not typically used.

If your dog is older, this method will not be as beneficial. Your veterinarian will consult a veterinary oncologist (cancer specialist) for additional or updated information regarding chemotherapy in dogs.


Spaying before the first heat or estrus cycle will greatly reduce the risk of developing breast or mammary tumors as compared to an intact bitch. Spaying before the first heat or estrus is also suggested as markedly decrease the development of mammary tumors in dogs.

Early spaying is the best method for prevention from mammary gland cancer. The risk of developing a mammary tumor in dog is 0.5%, if spayed before their first heat (approximately 6 months of age), 8% after their first heat, and 26% after their second heat. More than a quarter of un-spayed female dogs will develop a mammary tumor during their lifetime.

Living and Management

Your veterinarian or a consulting veterinary oncologist will recommend a treatment plan that includes management of your dog’s health at home with follow-up progress visits to the veterinarian or oncologist. Routine physical examinations and chest x-rays are required to check for recurrence or changes in the tissue after initial treatment. Surgery for tumors that is not spread may be curative.

For example, median survival after surgical removal of the breast or mammary tissue (mastectomy) with tubular adenocarcinoma is 24.6 months. Median survival after surgical removal of the breast or mammary tissue (mastectomy) with a solid carcinoma is 6.5 months. Benign tumors have an excellent prognosis after mastectomy.

Carcinomas that are less than five centimeters in diameter, usually have a good prognosis for remission, if the excision is complete. Involvement of regional lymph-node can be confirmed by microscopic evaluation, which make the prognosis worse and full recovery may not be possible.

Never ignore a breast or mammary nodule or adopt a wait and see attitude towards it. A breast or mammary lump should never be left in place and observed, as it can quickly metastasize when it is in malignant form. Carcinomas spread throughout the body and become untreatable before its severity is recognized. Early detection of cancer and complete surgical intervention is best.

This article is jointly written by Muhammad Hunain Ahmed, Sami Ullah Khan Bahadur, Muhammad Haider Ali

By Muhammad Hunain Ahmed

Student of M phil Pathology.