Call me a softee but when the rats here get tumors I usually retire them to either pet status or if it is severe I euthanize them. I had one such pet that lived to well past 3 years of age before the tumor got to a point it claimed her life. The last 18+ months she was not breeding and was simply a pet. I did this in the beginning to see if the tumor issue is heredity and it usually seems like it is. I have been able to breed out tumors in 90% of my colonies because I keep genetic data. I am also working on some odd ball projects like combining blue, double rex (ie hairless) and dumbo. Sorry I got off track. Anyway I don't feed the tumored up rats to the snakes in a nutshell.