large mass under arm

Question
I have a 1 1/2 -2 yr old dumbo rat named splinter, he is a very large boy. Friday I was holding him and everything felt fine but when I got home from work Saturday night I noticed he had developed a very large hard mass under his right arm that was not the 36hrs prior. He doesn't seem to be in any pain and is still active but he is like my son and I am very conserned for him. I'm currently looking for a good vet but until I find one do you have any idea what might have caused this growth or what it may be?? Please any information will be greatly appreciated.

Answer
If it is attached and hard, it MAY be an abscess.  Is there a scab on it or a hole or any pitting?  If not, it may be a tumor....which in that case would be a e a mammary tumor, which is not uncommon for males.  Sometimes they float and drop down which may be why you did not find it.  I can find a vet for you, let me know your location. The sooner it is removed the better if it is a tumor. If it is an abscess it should come to a head soon.  Check out my site, sandyscrittercity.com for info on both tumors and abscesses under the rat ailment section.