One of my rats got a cist (sp?) on his back. I decided to have it removed, just in case it was cancerous (it wasn't), and he healed up quickly and did just fine. He lived for another 6 months after that (died of pnemonia or some type of respiratory infection, totally unrelated to the cist)
On the other side, I had to have a hamster put to sleep (right around his second birthday), because he quickly grew a large tumor on his back that turned him hunchbacked and within a few weeks, he couldn't move at all. I also had a second hamster put to sleep because I had a tumor removed from his salivary gland area, and then he grew another tumor at the top his head less than a month later. The vet didn't think a second surgery was a good idea with the tumor being so close to his brain.
I think just about any small animal can get tumors. It just depends on their breeding.