My Cat Has Mammary Hyperplasia

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

By Arnold Plotnick, DVM | Posted: November 13, 2009, 3 a.m. EST

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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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My Cat Has Mammary Hyperplasia

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Reader Comments

Marta    International

12/30/2014 7:00:49 AM

Last December I adopted Akira, a 4-5 month old female cat. The day she came home I took her to the vet for a complete check up and he told me she was perfectly fine, and that we should wait until she weighted 2.5 kg. before we could spay her.
When she was barely 5-6 months old she got in heat for the first time. The vet told me that she had developed too early (he had wanted to operate on her before she got her first heat) and that now we should wait until she was done with her cycle.
Akira was in heat three or four times in a row, so we had to wait a couple of months before being able to operate her. During this time, the two mammary glands on her rear got significantly bigger. This didn't seem to upset her, she ate and played and did her business as usual. I thought this was normal for a cat in heat, with the hormones and all, and the vet didn't make any comments about it.
Finally, we were able to spay her. Everything went well, but the vet was a little concerned because her mammary glands got very swollen during the operation and, though he told me this was normal, he kept an extra eye on her.
For a couple of days, Akira's mammary glands looked huge, all red and swollen and she seemed to be uncomfortable. But then they went back to normal. Only that "normal" was still enlarged, since her pouch still dangles slightly from side to side when she walks, just as it did before she was spayed.
The vet told me there was nothing to worry about, he said that the fat on her breasts may be reabsorbed with exercise and a good diet.
However, though I've done as he said, it's almost been a year and Akira stays the same. I don't know if she has mammary hyperplasia, or if this is normal. I dont' know if she may need some kind of treatment or if she'll be just fine as she is.
What do you think? Thank you in advance for your time :)

Mark    Ireland, AL

5/26/2012 11:22:49 AM

My cat also has this problem. She has been treated with Alizin and the mammary glands seem to be getting better and her mood has also improved. She did have bad ulceration and necrosis on the two rear glands. The ulceration is gone now but the vet thinks there is a tumour. Does anyone else who has had experience of this know how the treatment progresses? How long until full recovery and how long to all the lumps return to normal? They seem softer now but there is a hard lump in the centre and they all hang quite low.

Mavis    Andrein, France, YT

3/24/2011 8:44:49 AM

The stray cat that came to me had this problem - breasts the size of small grapefruit. Had her spayed but it didn't help. Two breasts (then more) became ulcerated. Difficult to put dressing on this. They also started oozing milk which we thought was a good thing but the open wounds were a great worry. The vet asked to do a pretty major op on her but it was agreed there was not enough skin to cover the breast area. She was eating and looked beautiful in every way but I had to have her put down before she became severely infected and unhappy.

Anon    City, CA

11/17/2009 6:33:31 PM

Great information! I had never heard of this before.

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