Our rat Cocoa has a growth that I just noticed last night. It feels pretty soft when palpated, but is in a location that makes me think it may be a mammary tumor . It’s under her right armpit. How can I distinguish between an abscess (this seems to have appeared somewhat suddenly-in the last two or three days) and a tumor? At only about 10 months old, Isn't she a bit young for tumors? Thanks!