Those rats might well have gotten the same cancer sitting in a cage on someone’s desk, being fed lab blocks and taken out several times a day to be played with.
One of the sadder parts of keeping rodents as pets is they’re rather prone to developing tumors. Take rat cancer studies with a very large grain of salt.
Phthalates are being blamed by some for “disruptions of the endocrine system.” Whatever that is. Might be gay rats rather than cancerous rats.