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Mammary Cancer in Pets

October is Breast Cancer Awareness Month - which you might not have known is something that affects dogs and cats, too! Just like in humans, breast cancer in pets refers to tumors located in the mammary glands (although we usually refer to it as “mammary cancer” when talking about animals). In this blog, we’ll talk about preventative steps you can take to minimize your pet’s risk of breast cancer, how to identify symptoms, and what a diagnosis means for your pet.

Small dog standing in grass


What animals are affected by mammary cancer?

A number of companion animals, including dogs, cats, and rabbits, can acquire mammary cancer, though it almost always affects female animals. Mammary gland tumors are not always cancerous and can be benign (such as fatty lumps like lipomas). Mammary gland tumors are somewhat more common amongst dogs, but have a higher chance of being cancerous when found in cats. A common denominator amongst most pets diagnosed with mammary cancer is being unspayed or being spayed later in life.

How does being spayed affect a pet’s risk for mammary cancer?

Studies have found that an estimated 1 in 4 dogs who are not spayed and experience one or more heat cycles in their lifetime will develop mammary tumors. The good news is that mammary cancer is almost completely preventable by spaying dogs and cats before they reach sexual maturity (before their first heat cycle)! This is why we recommend spaying puppies and kittens between the ages of 6 and 9 months. Avoiding this first heat cycle all but eliminates the risk of developing mammary tumors later in life - even one heat cycle can increase the risk.

Are all mammary tumors cancerous?

Just because a tumor is found on the mammary glands does not necessarily mean cancer. Cancer refers to a malignant disease capable of spreading to other areas of the body, whereas a tumor can be either malignant or benign. Tumors may look or feel scary, especially when you discover them for the first time. To get to the bottom of what these new lumps are, reach out to your veterinarian. There are several ways to check out bumps and determine whether or not they should be removed. Unfortunately, there is no way to tell if a lump is cancerous just by looking at it or feeling it.

The first step when trying to learn more about a new mass is an FNA, or a fine needle aspirate. This is a quick and relatively painless procedure (just a quick poke with a small needle, similar to a shot) that can be done in office, usually with little to no sedation. An FNA allows your veterinarian to take a look under a microscope and see what kind of cells are located within the mass. While it can be difficult to determine if something is malignant (especially when it comes to mammary masses), it can confirm that the lump is associated with mammary tissue versus something else that could pop up in the same area, like a lipoma (fatty mass), for example.

Because any mass found on or near the mammary glands has the potential to be cancerous, we often recommend surgically removing the lump and sending it off to a lab for analysis to determine what kind of cells (benign or malignant) make up the mass. Histopathology will also be able to determine if clean margins were obtained (no remnants of harmful cells or tissue left behind) to make sure your pet is in the clear. If not all of the cancerous tissue was removed, a second surgery may be required.

What is my pet’s prognosis with mammary cancer?

If a mammary tumor is found to be cancerous, there are a few things that might affect your pet’s prognosis. The first concern is usually determining if the cancer has spread to other areas of the body. Mammary cancer can spread at unpredictable speeds, and spread to the lymph nodes or other parts of the body, like the lungs, worsens the prognosis. Additionally, the size and depth of the tumor can play a role - smaller and more shallow tumors usually have much more positive outcomes.

What are the treatment options for mammary cancer in pets?

In addition to removing cancerous tissue through surgery, there are other treatment options, including radiation therapy, chemotherapy, and antiestrogen therapy. However, usually, more specialized care is required for cancer patients. You and your veterinarian can discuss whether seeing a cancer specialist (oncologist) is right for you and your pet.

If you have noticed any new lumps or bumps on your pet, please contact your veterinarian to schedule a consult.

For additional questions please contact us at 972-347-6100.

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