You specifically asked for a doctor's opinion--and I am not that. But I do (like others on the board) have significant experience with this through loved ones.
It's hard to imagine any doctor recommendation at this point for Trey that does NOT include either chemo or radiation or both. And both are absolutely destructive to the human body. If either or both is what's next, it could be a serious while before Trey is back on a baseball field. He's a young man, in shape, otherwise healthy with the best doctors and trainers he could have, so there's always plenty of room for hope. My thought