Hello, I have a pet mouse, Rosie. About two weeks ago I noticed she had a lump on her backside, quite large. My uncle has had pet mice before and said a lot of them had tumors and that usually they weren't painful and that she may die soon. So i kept an eye on her, she played and ate and drank just fine, and didn't seem to be in any sort of pain at all. Now her body has doubled if not tripled in size and she can barely move. I picked her up and it looks as though her pink skin is almost a blackish color where her size is larger. She lays flat with her back legs out and can only drag herself with her front legs, i've only seen her move inches today and she hasn't eaten or drank anything. Any idea what i could be? She also seems to be breathing very hard and fast.