Second, if you do get bad news, don't change anything. Be honest with your employer, and go on with your life. At your age, chances are you'll be able to continue working through the treatment and long after that. It's unlikely that your company's premiums will go up, but that shouldn't concern you.
Third, if you do get bad news, ask the doctor for a professional to talk to. At your age, you need some guidance and perspective from someone you trust.