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Cats Can Get Breast Cancer Too

Mammary tumors in female cats are much more likely in unspayed females

October is breast cancer awareness month. Generally this awareness event is reserved for humans, but cats (and other animals) get breast cancer as well. In this article, I would like to tell you a bit about mammary tumors in cats, how they present themselves, and what you can do to prevent and treat them.

In cats, breast cancer is the third most common form of cancer, with the most common victim being a senior female cat around age 10 to 12 years that was never spayed. Unfortunately, 90% of feline mammary tumors are malignant with rapid spread to adjacent glands and the nearest set of lymph nodes. This sends the cancer into the blood and throughout the body.

At first the tumor is small and may feel like a pebble or dried pea. The tumor should be removed as soon as possible by a licensed veterinary oncologist. If left alone, mammary tumors get larger and harder and ultimately burst through the skin creating a smelly, infected ulcer. If removed without proper follow-up in the form of chemotherapy or radiation, there is a good chance it will return.

For some reason, Siamese cats have a higher incidence of developing mammary tumors. They also tend to develop these tumors at a younger age than other breeds (9 years is average for Siamese and 14 for non-Siamese).

Preventing Tumors

Early spaying is the most significant preventative factor. Spaying before age 6 months results in a 91% reduction in risk. Spaying before age 1 year results in an 86% reduction in risk. Spaying before age 2 years leads to an 11% reduction in risk. Having given birth to kittens has no effect on mammary cancer risk. Spaying after age 2 years does not reduce the risk of mammary cancer development at all.


To prevent re-occurance, chemotherapy is often recommended. Small "veins" of the cancer cells can root beyond the tumor, often missed in surgery. Later, these cells will develop into more tumors. The most common chemo drugs used are adriamycin and cyclophosphamide.

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