I have also had testicular cancer so I would like to tell you a few things about it.
While it is very aggressive, it is one of the most treatable cancers about. In my case it had spread to my lungs. I had the tesitcle removed followed by 4 months of chemo. This was over 10 years ago, my understanding is the treatment these days is much better.
While it is a concern that it has spread to his brain, this is also very treatable. Remember Lance Armstrong also had testicular cancer that had spread to his brain and he is currently running 3rd in the Tour de France.
Commonly this strikes males from the age of 28.
Best thing to do lads, is keep your eye on the ball.
Best of luck to John, I certainly appreciate that it is a frightening time, and while I don't have all the details of his case, the statistics are firmly in his favour for a full recovery