That's a bit extreme. He has already under one round of chemotherapy, and is to be treated by an oncologist who is board-certified in radiation therapy, and has indicated he may undergo radiation therapy and/or immunotherapy. Yes, he might be dead within a year, but it's far from certain, and more chemotherapy wouldn't be a guarantee either, especially since he had an especially bad reaction to it the first time. Quality of life matters, and it's not clear that he won't get more of that by going his chosen route, even though he'd very likely get more quantity of life with the chemotherapy.
"He since has been using an alternative herbal treatment called the Hoxsey method, the sale of which was banned in the United States in 1960."
The "alternative treatment" to be provided by his board certified oncologist may work, but it's a big risk. It's going against the odds.
If we were talking about some senior citizen who had pretty much lived out his life I could understand it better but this is a 16 year old kid who could have a long life ahead.
Just my opinion of course but I'd rather my son have the 85% chance.