Mai Rat Haz Cancer? What do you think?

So Mis[t]y, female rat, is almost 3 years old. I've had alot of rats but she's the only one that has had a growth so early. Two bumps, one on the stomach, and one under the armpit (or on the armpit). She's very healthy otherwise, clean fur, plenty of exercise, but im wondering if her diet might be causing it. It's made up of peanuts, fruits, and the occasionally M&M. And she enjoys swimming! lol What can I do to get rid of the killer growth. I can't have her do surgery because I don't have the money. Any suggestions, or should I just wait it out? Thanks