If you go to a well known and respected breeder who knows their lines you will have very minimal problems, if any at all. All of my breeder rats are healthy, sept one who just had a seizure due to unknown reasons but it hasn't caused any other damage and he's perfectly fine. He's also one of my old guys anywho. The vet suspects the peanuts, so....I would really urge you to get breeder rats, as pet store rats have MANY problems, as YLL can tell you. They are NOT bred for health in mind at all! Nice quality breeder rats can live up to 4 years if you take good care of them. It mostly is dependent upon the owners care for them. If you don't clean the cage enough the amonia will build up and then they will get respiratory problems etc. I've never had a doe with a tumor, ever. Wrinkles, my hairless girl is going on three years old and is doing great. She does have the occasional Myco outbreak but she is from a petshop so that is to be expected. I have only had problems with health in pet shop rats, such as my Bandit, who gets constant Myco flareups about every day. But the love they give you in return is so worth it!!! Of course, there are breeders out there who don't give a crap about their animals, and those rats will have tons of issues, with both health and temperament.