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Answers from vets about your cat:

Mammary Tumors in Cats

Posted July 23, 2015 in Cat Diseases & Conditions A-Z

AJ Debiasse, a technician in Stroudsburg, PA, contributed to this article.

One of the reasons veterinarians recommend spaying cats is that it is an easy, affordable and efficient way to prevent mammary or breast tumors. These tumors are a huge problem for cats. According to the American College of Veterinary Surgeons, 85% of them are cancerous (i.e. only 15% are benign!)

Orange cat on counterWhat causes mammary tumors in cats?
Mammary tumors develop because of spikes in female hormone (estrogens) that take place during a cat’s heat cycle. By spaying a cat at 6 months of age or before her first heat cycle, it virtually eliminates the risk of getting mammary tumors.

What if your cat already has mammary tumors?
Since spaying prevents mammary tumors, should a cat older than 6 months with mammary tumors be spayed? Yes, without any doubt. Again, spaying at that age will not prevent mammary tumors. However, it will eliminate the risk of pyometra, a life-threatening infection of the uterus. Therefore, if you are in this situation, you should have an open discussion with your vet, understand the pros and cons, and decide what makes the most sense.

How will your veterinarian check for mammary tumors?
Most mammary masses are found on a physical exam by a veterinarian. Occasionally, a mass is found by the guardian or by a groomer, especially in a cat who enjoys belly rubs. Most masses are not painful. When they outgrow the skin or rub on the floor, they can become ulcerated, which means that the skin has opened up and the mass can bleed.

How can we tell if a mammary mass is benign or cancerous?
Looking at a mass, or feeling it, doesn’t help us determine the diagnosis. The only way to diagnose the type of mammary mass is by taking a biopsy and sending it to the lab for analysis. In most cases, the mass is surgically removed first, and then sent to a pathologist.

How will your veterinarian decide whether to biopsy the mass first or not?
How do we decide whether to biopsy first or not? As a general rule, I recommend taking a biopsy first if there is a chance it will change the treatment plan. Since the vast majority of mammary tumors are cancerous in cats, the question is hardly ever “is it cancer or not?” but “do I want it if off my cat no matter what it is?”

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Dr. Phil Zeltzman is a board-certified veterinary surgeon and author. His traveling practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at, and follow him at