Incidents of cancers have been found to commonly occur in rats.
To a lesser degree they have been found to occur in tree squirrels cared for in captivity, this mostly associated with obesity, but also with infections.
This procedure to remove a large cancerous growth from the intestines of a rat, and resection the bowel, was successfully accomplished.
Rather amazing to see this done on such a small animal, yet with todays technology it is now possible. Warning this file contains photos of graphic content!