Quote Originally Posted by GreyhoundGirl
What would get smaller by itself. Cancer wouldn't. Would cists?
Mast cell cancer would. The hallmark of a mast cell tumor is that it changes size regularly. My Paxil has had mast cell cancer twice. The first tumor would go from the size of my fist to a the size of my thumb in the course of a day or two. The second time she had two tumors, much smaller ones, but they grew rapidly, especially once they were touched. The tumors were removed and Paxil is fine now.

The only way to know for sure is to get her to a vet and get a biopsy done asap. If it is cancer or something serious, the longer you wait, the harder it becomes to treat successfully.