Hi Anna:

My cat (female) also had a lump on her tummy. It was an inch or two in diameter and ended up being a benign tumor. I guess they are pretty common and tend to develop in fatty tissues. Since she developed this when she was an older cat (she was eight or so) I decided not to have it removed and it never bothered her or developed into anything serious (though it did get a little larger -- it was pea sized when it began). Your vet can easily take a bit of fluid and test to see if the cells are worrisome. I'd recommend it, just to make sure. Good luck to you and your furry friend!!