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Mice/Lump on mouse lower abdomen


Hello, you have always helped me with my mouse related issues in the past. Currently I have a female mouse who is just a bit over 1 years old (her cagemate died a few months ago). A few days ago I noticed a lump near hear bottom and it has increased in size over the past few days. It is not hard or anything but is pretty large. Here is a link:

I was wondering if you ever saw anything similar. I know tumors are very common in mice, but mine never had tumors before.

Any advice would be greatly appreciated. Thank you again in advance.

Hi Stephanie,

Any lump is usually an abscess, tumor, or cyst. And though I thought it looked low, my breeder just told me (I showed the photo to a few people) that he has had one there.

However, in that location it can be also a problem in the urinary tract, or of the urinary tract. Is she peeing normally?  Another breeder friend had a mouse with a lump there which turned out to contain urine. She was able to express the urine (squeezed it and the mouse peed) sometimes, but in the end the mouse had to be euthanized.

I would like to know if it is centered or lopsided.

My recommendation is to go to the vet. They should be able to diagnose it and if possible, treat it. It is not a nice place to have or deal with a problem. An abscess there might also be difficult to deal with.

The two things I would do before the vet appointment, which should be within a day or so, is 1. gently squeeze it to see if she pees, and 2. assuming she doesn't, apply a hot compress to it for ten minutes 3 times a day. An abscess should come closer to the surface, possible turn dark, and may even rupture with such compresses. She can take any heat you can. If it ruptures it may be disgusting (including smell), and you will need to keep it clean and open.

If it turns out to be a tumor, I don't recommend surgery, but it may be an option you consider. I don't recommend it because mouse tumors are almost all malignant-- cancerous-- so they come back. And come back. Especially mammary tumors, which is what that would be if it is a tumor. The last time I had one removed and the mouse survived the surgery (there is high risk of death from surgery; certainly less now than there used to be, but still it can happen easily) she got two  more tumors within a week. Needless to say I no longer have surgery for tumors. The last mouse I had who had a tumor, which I did not remove, had had-- upon inspection after death-- three more mammary tumors on the way.

If it comes to the question of euthanasia, you have to ask yourself about her happiness. When my mouse or rat is nearing the end and may need to be assisted, I "ask" them every day "Are you happy to be alive today?" Recently the answer from a very, very special rat was "mommy, just make the pain go away, please" and so, my heart broken and not ready to lose him, I  made the right choice for him. With her, if it comes to living with a tumor there, it may not be long before her quality of life is too compromised to be worth it. She won't be happy if she can't walk or clean herself.

I hope it turns out to be something fixable... do let me know.



PS if I get any more information from my breeding and/ or medically knowledgeable (mostly rat oriented) friends-- there is one good mouse breeder whom I did not yet reach who may be able to help; and I posted in my FB mouse and rat group and may get a different response-- I will amend this answer and you will get an email notification. But I recommend making a vet appointment now.  


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I can answer questions about raising mice and caring for them as pets, with knowledge from my 38 years of having fancy mice as pets. I have NO MEDICAL TRAINING and you should take a sick mouse to the vet; but if you simply can't, I will try to help you. I LOVE PHOTOS!!! I ALSO LOVE UPDATES! Let me know how the little tyke is doing later on, for better or worse, especially orphans. It also helps me to help the next person. Please first search first: use 'Natasha Mice Mouse' with whatever else your question includes. Or check out these links: **** YOUR FIRST MOUSE (my video; rough draft): **** TEN VIDEOS ON RAISING ORPHANS: **** SEXING MICE: **** And some GREAT MOUSE INFO SITES:


I have had mice for 40 years (since I was 5!). I raised them when I was a child but now I keep all females, and never fewer than three so that if one dies the others are not devastated, because they have each other.

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B.A., M.A., M.A. in Linguistics: Yale University and University of Connecticut

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