I'm really sorry to hear about this Tim. My aunt had breast cancer about 10 years ago. She had surgery and chemotherapy. She's still doing very well to this day, no new cancer has formed and she has no long-term affects from the treatment.
My high school friend's mother had breast cancer back in the late 1970s at a young age. She's still alive and kicking after 3 decades.
Just be positive and support your mom with anything she needs and hope for the best.