Mammary Gland (Breast) Tumors in Dogs

Overview of Canine Mammary Gland Tumors

Mammary gland tumors are a type of cancer that arise from breast tissues. These tumors are similar to breast cancer in women, and they can be lethal in dogs. Approximately 50 percent of these tumors are malignant, which means they can spread, and 50 percent are benign and do not spread.

The cause of mammary tumors is not well understood. Hormones such as estrogen and progesterone play an elusive role in the development and progression of these tumors. They occur in both intact (non-neutered) and spayed dogs and it is the most common cancer of female dogs, with two cases per thousand dogs at risk, constituting over 50 percent of all cancers. Mammary gland tumors occur most commonly in females; they are rare in males.

The average age that dogs develop these tumors is 10 to 12 years of age. Any breed of dog may develop these tumors, but breeds that appear to be at increased risk are poodles, terrier breeds, cocker spaniels, and German shepherd dogs.

Timing of ovariohysterectomy, which is removal of the ovaries and uterus and commonly called neutering or spaying, significantly impacts development of mammary gland tumors in dogs. Dogs spayed prior to their first estrus cycle (heat cycle) have less than a one percent risk, those spayed between the first and second estrus have an 8 percent risk, whereas those spayed after their second estrus cycle develop these tumors as commonly as dogs that are not spayed.

Body weight may influence the development and progression of these tumors.

What to Watch For

Signs of mammary gland tumors in dogs may include:

Diagnosis of Mammary Gland Tumors in Dogs

Treatment of Mammary Gland Tumors in Dogs

Home Care and Prevention

If you note a mass in your dog’s mammary glands, have her examined by a veterinarian as soon as possible. Malignant masses that have gone undetected for long periods and are large are more likely to spread.

If your dog has a large, ulcerated, bleeding mass keep her indoors to keep the area clean and lessen the potential for infection before seeing your veterinarian.

Have your pet spayed or neutered at an early age to decrease the risk of this type of cancer. Avoid the use of synthetic hormone products to control heat cycles as they may increase the risk of your dog developing this type of tumor.

Take your dog to your veterinarian for regular examinations so that tumors can be detected early when they are more likely to be completely removed. This is especially important if you have an older dog that is at increased risk for this type of cancer.

In-depth Information on Mammary Gland Tumors in Dogs

Swelling of the breast tissue can be related to a number of conditions – both normal and abnormal. For example, normal hormonal changes associated with the female reproductive cycle in nonspayed females lead to enlargement of the mammary glands. Pregnancy is of course related to glandular development. Inflammation, hyperplasia (excessive growth), and cancers are examples of abnormal growth. When mammary glands are enlarged or swollen, a veterinarian will consider a number of diagnoses.

Veterinary care should include diagnostic tests and subsequent treatment recommendations. Medical tests are needed to establish the diagnosis, exclude other diseases, and determine the impact of the mammary gland tumor on your dog.

In-depth Information on Diagnosis

Your veterinarian may recommend additional diagnostic tests to ensure optimal medical care. These are selected on a case-by-case basis.

In-depth Information on Treatment

Follow-up Care for Dogs with Mammary Gland Tumors

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical. Administer prescribed medications as directed, and be certain to alert your veterinarian if you are experiencing problems treating your dog.

Specific optimal follow up veterinary care for mammary gland tumors in dogs and cats involves the following: