Rat Tumor or Cyst?

Question
My female rattie Lilley is 1 1/2 yrs old. Recently she developed a growth the size of a small cherry under her right front leg. It is somewhat movable. In a matter of a week it looks to have gotten slightly larger. She does let me still scratch and play with her as if it's not a tremendous bother to her. I was told by a vet that it could be a tumor or cyst.  If it is a cyst he could aspirate it. He didn't answer the question would it need to be aspirated again and again. As the charge is $100.  This is something I think I should know. If it is a tumor I prefer not to do surgery as my last girl died during surgery.  I prefer not to put my girl through any more trauma than is necessary. Should I just let her live out her life until she needs to be put to sleep? Or do I put her through what I believe is painful procedures? Thanks you for your time.

Answer
Hi Deb,
It is probably a benign mammary tumor. I'm in the process of posting an article on my website about a high-fat calorie restricted diet which shows promise in shrinking tumors. It is fairly involved, but might be a good option to surgery. I hope to have it all up on my website at www.ratfanclub.org by the end of the day. Right now I'm having a problem with the pictures.
Deb