Some "natural" products like Yew are already used in chemotherapy to treat cancer.
Just because a product is "natural" does not always mean it is safe (i.e. Cocaine comes from a coca plant).

The Graviola plant can kill nerve cells in the brain and other parts of the body. It may cause movement disorders similar to Parkinson’s disease.

There are pros and cons to many treatments - natural or not - it's up to each individual to do their research and decide for themself. Just don't create false hope for those battling cancer.