I would just get as much info on the situation as you can and as well as offering emotional support (if your up to giving it) see if theres anything you can do practically to help, whether this be talking to the doctors or running errands. Its the small gestures that are often appreciated the most so just be there in anyway u can and im sure your boyfriend will be grateful. Good luck.

Edit: and remember if ur bf doesn't want to discuss the issue don't push it, he'll come around in his own time. Or if ur finding the opposite is the case and he wants to talk about it more than your comfortable with you have to try and be honest about that. Your wellbeing is important in this situation too and if your not feeling as strong as you can be your probably not going to be able to support him as well as you'd like providing of course he wants the support. Again good luck.