I'm sorry to hear this Tooya. At least you know you're not alone ^^^^ . So many people have been affected by cancer in some way or another. I wanted to reply yesterday but I'm managing with similar news myself really. My mother was diagnosed with Non-Hodgkins Lymphoma many years ago and she completed her course of treatments twice and her cancer went into remission. Unfortunately this past week her doctor informed her that it's active again. I'm happy to note that my mother is feeling rather confident as the doctor said it's curable.
Try to be as supportive as you can and I wholeheartly agree with Gypsy's advice; "It is important your mum knows you care, but she does not need to be more worried about how you are coping than herself."
We are what we think. All that we are arises with our thoughts. With our thoughts, we make our world.
“When I let go of what I am, I become what I might be.” – Lao Tzu