That's not usually true. A large proportion of pet rats die from tumours. Furthermore although e.g. in mice, there's Oncomouse, bred with a susceptibility to

That's not usually true. A large proportion of pet rats die from tumours. Furthermore although e.g. in mice, there's Oncomouse, bred with a susceptibility to cancer, rats have been resistant to similar techniques (https://en.wikipedia.org/wiki/Knockout_rat#Production_challenges https://en.wikipedia.org/wiki/Knockout_rat#Production_challe...)