Have Microbes been found inside of cancerous tumors? Maybe, maybe not.
We know that Cancer is a constellation of diseases, and at least some,
per the HPV vaccine, are caused by infectious agents. What percentage of
cancers, and of which types, are or are not generated by microbes is a
big deal for future study. (Beyond the flaws in studies claiming microbes have been found inside cancerous tumors, even if true, we don't know if there's any causation behind the correlation, of course. And, even considering that possibility, without further evidentiary guidance beyond correlation, we would have no idea in which direction the causation proceeds.)
Meanwhile, we're learning more about contagious cancers. Yes, as in cancers that, whatever the cause in an individual animal, can be transmitted from one to another.
This is why scientists and science journalists talk about the provisional nature of science.
Plus, this all has public policy effects. Where do we spend government cancer research dollars, for example?