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Pet Rats/Tumor..popped up after eating?


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Hi Debbie,

It appears my male rat Ziggy, who is a little over two years old, has developed an odd lump on his side. I've already read the pages on your website regarding determining whether the lump is an abscess, tumor, or cyst..but I still can't figure out what it is. A few days ago I noticed he had very raspy breathing, so I took him to the vet and they prescribed Baytril and it surprisingly cleared up overnight. The next morning his lungs sounded completely normal, but I am continuing the Baytril of course. I recently gave him a treat of Nutro Natural Choice weight management canned food for the first time and I picked him up a few minutes later (after he gorged out on his snack) and noticed a large bulge protruding from his middle right side. I figured maybe he was just "full" and put him back. I checked on him again many hours later and the bulge was still there. I know it is not a blockage because he has pooped since the feeding and continues to eat and drink normally. He doesn't appear lethargic or any less active than usual. The lump is relatively soft and moves when he scratches almost like a ball of fat. I'm guessing this means it moves with his skin. It does feel a bit hard in the center. From the pictures on your website, I am 99% sure it is not a cyst...but it would be odd for a tumor to just show up in a matter of hours. I'm going to include a picture because maybe that can help you. Thanks so much.

Hi Lily,
It appears this lump just under the skin, is that correct?  It is most likely a fibroma, which is the most common tumor in male rats. Did the vet give him a full exam? I'm going to guess not, or he would have found the lump. It is not possible for a tumor to just appear after he ate something. The lump was likely there but you hadn't noticed it.  But some tumors do grow quite quickly, so it was no doubt larger then than it was the day before.

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Debbie Ducommun


I can answer any questions about pet rats, but you will probably be able find answers to simple questions more quickly on my website at If you have a life-threatening emergency you can try calling me at 530-899-0605. I am not usually on the computer on the weekend.


I have been "The Rat Lady" since 1985 and am recognized as one of the world's experts on pet rats. I have 3 published books and already answer lots of questions about rats daily.

President of Rat Assistance & Teaching Society

I am a monthly columnist for Pet Business magazine, and my writing has appeared in other magazines. I have 3 published books.

BA in Animal Behavior

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