George Harrion's battle with cancer started in his lungs and throat so one can reasonably argue his smoking probably contributed to it, or at least it certainly didn't help matters. His brain cancer was not a primary cancer but was rather a metastatic cancer, spreading there from the other sites. While they don't really know what causes brain cancer, I don't think they're seriously looking at smoking, of course, since smoking has been shown to be dangerous to one's health I don't think they've ruled anything out.