Oh Kate I'm so sorry to hear that. It really is a shit of a thing this breast cancer. So many of us find more than the mammograms and ultrasounds ever show, myself included. My tumour turned out to be twice the size the mammogram showed. I had a wide local excision, a re-excision for margins, and in the end (months later after chemo) a double mastectomy and reconstruction.
The only thing I can say is at this stage focus on the end result, which is a body free of cancer. Mastectomies tend not to be too painful so put that worry out of your head. Are you thinking about reconstruction?
Take some deep breaths, they help calm the nervous system. And if you want to, tell us a little more about yourself, and your diagnosis.
Hang in there fellow Kate. K xox