Sorry you find yourself here and in this situation. I would say be honest with your Mum about your feelings and anxieties. She may be able to reassure you. I recently had to tell my children about my recent cancer diagnosis and found it much easier when I knew how my children were feeling and dealing with it, and what support network they had. As I'm sure your Mum will be worrying about you as much as she is about herself. Ask questions, discuss your Mums treatment plan - all of which might help both you and her. Try not to  bottle things up, use this forum, a good friend or even write down your feelings. Take care x