The ancient healing arts knew this, you might want to investigate how Tibetan medicine dealt with tumors. (Tibetan med is something the Chinese, when they invaded, did not burn to the ground, as it was older, and better than TCM was at the time).

I was privy to how an artist who got a surface cancerous tumor dealt with it. As a painter he was exposed to toxic substances used in their paint. Once the toxic stuff was in the tumor, the issue is how to get rid of it. TL;DR they made an infectious concoction - of a very specific formula - that is carefully applied to the tumor, and it is allowed to fester for weeks under care until it has dissolved.

I watched it work. Internal tumors are dealt with in different ways. Ppl with $$ knew, incl. Bill Hall of Hallmark (you can look that up), but by the time he went to them it was too far gone. Many wealthy have been treated. And kept it quiet so as not to get shut down.

Needless to say, don't try this at home.