Hi
Yes, both mice & rats are prone to tumours.
As a kid, one of my mice had a lump nearly as big as himself, grew fast & had to be put down, his brother had it too.
Some strains of mice & rats are more prone to them, then other strains. In lab rats ect, it's bred into them for research purposes.
We had rats opperated on for lumps, but they always went downhill fast afterwards & died within months. We wouln't have them opperated on now, we would watch them to see they are happy, no pain & no ulcerations & put them down when the time came.
Sorry to be so negative.