I just finished "The Secret" by Rhonda Byrne. It’s all about visualising
your goals.
Now if you have cancer, I don’t think you can cure yourself by just visualising that you are healthy again. If you have metastatic liver cancer, I won’t believe you can get cured just by visualizing. But it is just another little "medicine" if you are on the road to recovery.
Visualisation works far better for prevention of diseases: keep on visualising that you have a good health.
It’s not a miracle cure, but if every day you program your brain to be more healthy, you will after some time start paying more attention to all things health and you will make more healthy choices for your future life.
Summarized: the secret is just focusing on what you want and reminding you about it every day!