Well, that is a drawback in any kind of research. Sticking with animals and cells, we can use very rigorous methodology, ensuring that each study group is identical, save for the variable under study. However, it is not ethical to study humans using that same rigorous methodology. So we are stuck with establishing carcinogenicity in animals and trying to analyze whether the same effect is true in humans without actually testing on humans. The more carefully animal or cell studies are designed, the higher the likelihood that the results will be applicable to humans.
Allow me to clarify then...
It would seem that the exact pathway is still an unknown.
Is there a specific animal protein based benzene/amine sequence processed by the human gut and passed to our cells that can trigger cancerous mutation? It would “seem” that such a pathway exists in other species... But it is still an unknown for us...
My Uncle was a bio-chem scientist who lost a two year battle with pancreatic cancer. It’s given me a renewed interest in the topic.