A similar situation has happened here at work, twice. Although I wasn't friends with these guys as long as you have been friends. I didn't know a certain coworker had cancer, they were out for a while, came back and he was unrecognizable, very thin, weak looking, and I was in shock when I realized who it was. A month or so later, that person passed away. Now, another coworker has it, and is going through similar stages. Its very discouraging to see this happen....