[mberning]

It doesn’t seem completely out of the question that he could have received a contagious cancer. There are examples in the animal world. I believe Tasmanian devils spread facial tumors through biting. And I have heard dogs have certain transmissible cancers as well.

[mapontosevenths]

It stands to reason in my decidedly non-expert opinion. Many cancer cells have "forgotten" how to differentiate properly. Why should such a cell care if it's in the proper host any more than it cares it's in the proper place within that host?

I am a bit surprised that his own immune cells wouldn't stop it, but if cancer were easy for the immune system to deal with nobody would die of it.

[sokols]

> but if cancer were easy for the immune system to deal with nobody would die of it.

This made me think, whether it would somehow make sense that cancer cells on another host would be detected by the immune system of that host. Theoretically, these immune cells have different “initialization parameters” so to say and maybe they could show affinity to the foreign cancer cells.

But then again I am not an expert and this is just a pure speculation.

[golem14]

Healthy transplants from other organisms are also attacked…

[pfdietz]

The dog cancer is not fatal though, I understand. The immune system does eventually fight it off.

Tasmanian devils apparently have little genetic diversity so they are more subject to this problem.