I suggest finding a new holistic doctor. I don't think there is such a thing as an unbeable cancer, though there may be many cancers that the holistic doctor does not know how to beat, the same as there are many cancers that mainstream medicine does not know how to beat. That does not mean that they cannot be beaten and I would bet you right now that you cannot find a single kind of cancer that someone has not beaten.
How dare that doctor to tell you that just because of his own limitations!
Now, there certainly are cancers that are more difficult to beat and/or more agressive. In which case you should not try to beat them with half measures. In other words, accept it as the life or death battle that it is, go all in and throw the book at it with an all encompassing anti-cancer diet, lifestyle, supplements, stress management, etc. Don't let up for a single minute and believe in your plan. I bet if you do, it will work.