If you have a dream of you dying of cancer it means that you are worried about your future and the fact that you are aging. Usually a dream like this happens to someone in middle age. This is because people that are elderly are generally the people that end up getting cancer. When you put your heart and soul into something and try as hard as you can to make sure that your life is not wasted you will find that you will succeed well in life.
You just need to calm down and stop worrying about aging. The thing is, it is perfectly okay to be afraid of aging because aging brings death. It is also totally natural to be fearful, but at the same time you need to realize that the more you worry, the less rational it becomes and the more of a waste your life becomes. If you spend all your time worrying about what could happen instead of thinking about what is happening now then you will have wasted the time that you did have instead of living it up to the fullest before you were too old to be able to do that. Do you really want the later years of your life to be a waste or do you want to make the most of it all and see what you can do to succeed. For most people, this is a no brainer. All you need to do is calm down a bit and stop worrying about having cancer or dying of cancer.