My sister's rat Violet has had this issue for a while. It only has gotten worse over time. She took her into the vet a while ago and the vet said it was a cyst. However, I think it's might be something worse like cancer or a malignant tumor. Warning: the pictures are a bit gross: The first 5 images below were taken on November 24th. The following 4 pictures were taken tonight, December 8th. As you can see, it got worse. She's on baytril. It also smells bad. Especially when she pees. She's still active surprisingly and does not show symptoms of pain. I told my sister that she should consider/get ready to put her down. Any thoughts?