Getting the tumor removed should actually improve his health beyond the eyesight problems he was having. He is going to finally stop growing. Choi is already so big that I'm sure he will have horrible problems with his joints and bones later in life and his heart is probably already damaged but at least he is stopping the progression.
I hope that the surgery is a success and the doctors are able to get the entire tumor or he could need further surgeries.
Credit to Toxic for the sick sig!