Can my pet get breast cancer?

As most people know, October is National Breast Cancer Awareness Month. All month long we will see pink t-shirts, ribbons and signs for various walks and fundraisers to shed light on this serious and sometimes fatal disease that will affect about 1 in 8 (roughly 12%) women in the U.S. each year. Our pets, unfortunately, are not spared from this scary diagnosis.

Mammary gland tumors are the most common tumor diagnosed in female dogs, and the second one found in female cats. Spaying a dog before her first heat cycle decreases her chances of developing mammary tumors to 0.5%. Waiting until the second heat increases the likelihood to 8%. Spaying after three or more heat cycles increases the risk of mammary tumor development to 26%. Early spaying in female cats can reduce the likelihood of developing mammary tumors up to 50%, but once she passes 1 year of age, the time frame for spaying will not decrease her chances of mammary tumor development.

Compared to women, our pets have more breast tissue at risk for tumor development – dogs have 10 total mammary glands and cats have 8. Each of these glands is a potential site for tumors based on gender and age. Typically, tumors occur in the last two mammary glands but can develop in any of them. Cats and dogs are equally as likely to develop a single mass as they are to develop multiple tumors in multiple breasts.

Dogs and cats also differ in the prognosis of their tumor types. While dogs fare better with 50% of tumors being malignant and 50% being benign, about 85% of feline mammary tumors are malignant. In both species, the odds are not in the patient’s favor. The best course of action is complete surgical resection, often requiring removal of mammary glands above and below the affected one as well. All patients should have full lab work performed, as recommend by their veterinarian, along with x-rays of their chests to look for evidence of metastasis, or spreading, into the lungs. Lymph nodes in the groin, arm pits and in front of the shoulder should be palpated thoroughly to examine for potential spread as well. Follow-up with a veterinary oncologist should be considered to see if your pet is a candidate for chemotherapy or radiation therapy.

The best thing you can do for your kittens and puppies is to spay before their first heat cycles. This will minimize the risk of mammary tumor development later in life. It is also a good idea to periodically feel and check every single one of your pet’s mammary glands to look for any lumps and bumps in the breast tissue—double check the boys also because cancer doesn’t always follow the rules. Men get breast cancer too! If you feel anything abnormal, be sure to bring your pet to the vet as soon as possible to have it evaluated and removed if necessary. These procedures should be performed at full service hospitals for appropriate pre- and post-operative care.