I first take exception to the "the enlightened" because if anyone were "enlightened" they wouldn't be here. They would have completed their lessons here on School House Earth and gone on to other things. There are many people who have a facade of enlightenment and truly have some great spiritual achievements, but many times they have missed some very basic steps that they will have to come back and learn before their journey is complete. I know nothing of your cancer guy, but I agree that Cayce in particular was a very high spirit. (Gandhi too was a high spirit, that's how he got the title of Mahatma, or high spirit.)
Bodies die. We each choose where and when we will be born and who are parents and siblings will be. We also choose the way that we will die. Then when we die we either go on to other planes for more learning and/or return to this plane in another body. Our bodies want to be eternal. They are not. Our bodies, if we are not in control of them, go into fear when others die because it reminds them that they are temporal. We as spirit have to remind them that they are our temporary residence while we are here to learn, and we have to treat them with respect during the time that we own them.
Just because there are entities in bodies on higher levels of learning than others, does not mean that they are without illness or even early death. I think an excellent book on the subject of reincarnation and why, is "Many Lives, Many Masters" by Brian Weiss, a psychiatrist who learned a great deal about the topic from one of his patients. During her trip through regression (his first patient who regressed into an earlier life) he discovered even many things about himself including the fact that his son who died at age six weeks of a very rare condition was in fact a highly developed entity. Age or what we have appeared to learn have little to do with where we are really at in our spiritual evolution. That book by Weiss is the first of many that he has written on the subject.
I know nothing about the guy you mention who died of cancer but I've read and am familiar with Edgar Cayce. Cayce was a Pentecostal Sunday School teacher until his death. It may seem like a dichotomy and it even was for him for a while, but the further he went in his readings, the more he recognized that there was not a conflict. Cayce gave a great deal of himself away - for free. He was a huge giver. In some cases he made others wealthy. In fact he spent little time on his own basic needs and more on his readings which he felt was his calling, all to the chagrin of his wife. Near the end of his life he was in much need of a lot of rest and instead of rest, he gave more. He did more and more readings because he felt that he had to heal others.
All entities die, regardless of their level of "enlightenment." Everyone of us choose the moment and the way we will die.