My Cat Has Mammary Hyperplasia

CatChannel veterinary expert Arnold Plotnick, DVM, discusses the condition, and what can be done to alleviate discomfort.

Q: I have a 1½-year-old female Maine Coon who has generalized mammary hyperplasia. She had her first heat 2½  months ago and was bred immediately to her proposed mate. She began at once to develop this breast swelling which quickly became quite large and uncomfortable. Her breasts actually were the size of grapefruits and had begun to abscess. We opted to spay her in hopes of reducing her discomfort. The swelling did not respond to the surgery, but the hardness and tenderness resolved. It has been over a month since her surgery and my vet has given her a testosterone injection as a second attempt to reduce the swelling.  Do you have any idea what might be going on with her endocrine system and what can be done to eliminate this pendulous breast tissue?

A: The condition you describe, mammary hyperplasia, is characterized by rapid growth of mammary tissues. It tends to occur in young, unspayed female cats. Mammary hyperplasia occurs as a result of the influence of progesterone on the mammary glands.

When a young cat becomes pregnant (ovulation followed by fertilization) or pseudo-pregnant (ovulation, but no fertilization), progesterone levels begin to rise. Mammary tissues in cats have many progesterone receptors, and the binding of progesterone to these receptors can stimulate mammary gland development.

Although the condition is generally regarded as benign, in some cats, this stimulation can lead to severe swelling, pain, ulceration, and infection of the glands. Treatment involves removing the source of the progesterone, although frequently, removal of the progesterone doesn’t result in regression of the swelling. In the case of unspayed females, removal of the progesterone source is best accomplished by spaying. 

The extent of the mammary gland swelling, however, can make a relatively simple surgery like spaying much more difficult.  The swollen mammary glands tend to be very painful, and in my experience, the incision site often becomes bruised and very tender afterward, causing a lot of discomfort for the cat.  It sounds like your cat came through the surgery OK, which is fortunate. A few years ago, I had a case of mammary hyperplasia that was a disaster. The client had unfortunately waited several days before bringing in the cat for examination, and by the time I had a chance to examine the cat, several of the glands had ulcerated and had become seriously infected.  When this happens, it is sometimes necessary to surgically remove the swollen and infected gland(s).  Unfortunately, this cat, with a high fever and severe dehydration, was in no condition to be anesthetized for any type of surgery.  Emergency care with intravenous fluids and antibiotics was unsuccessful, and the cat developed septic shock followed by cardiac arrest. She could not be resuscitated. She was only 7 months old.

It can take quite a while (weeks, sometimes months) for the swelling to resolve after surgery. A few years ago in CAT FANCY, I wrote about a progesterone-blocking drug called aglepristone that showed great promise in treating this condition.  Sadly, the drug is still only available in the European Union, and not in the U.S. Testosterone injections are unlikely to help your cat. Warm compresses (a washcloth, soaked in very warm water, then wrung out and held on the swollen glands for 10 minutes, twice daily) may help reduce the swelling, but otherwise, this is something that will hopefully slowly resolve over time. 


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Cats · Lifestyle