I would be careful with that if I were you. The same thing happened to my Dad.
He had Colon Cancer, and my brother convinced my Dad to become a born-again Christian and so he believed he would be healed of his Cancer. Same thing, a very well-known "man of God" helped him. The doctors all said his Cancer was completely gone. My Dad was convinced that he was completely healed as was everyone else.
About a year later he had some bad pains in his body. It turned out that the Cancer had spread everywhere to his liver and other organs. The doctors gave him 2 weeks to live, and that was it, it was over.
I'm not trying to disregard your faith or anything, but it's imperative that your son line up a good Alternative Cancer treatment and start now, a good Rife Machine at this point, the Rife Forum here is a good place to start.
Maybe God needs some help to help your son. The saying that God helps those that help themselves comes to mind. I hope that makes sense.