Like everyone else, I'm really sorry to hear your news.
A friend in may dive club also went through the same a couple of years ago. She is an instructor and was OK to dive again after the masectomy and chemotherapy that she had. I don't know all of the details though.
I recommend speaking to a dive doctor. London Diving Chamber give free email advice, which could be a good place to start -
doctor@londondivingchamber.co.uk