Good luck to you both!
I will say that both my mom and her sister were long term breast cancer survivors, one lived to 93 and the other to 96. My aunt took something called Tamoxifen, and that might have had something to do with it. Though at 84 she survived colon cancer.
Neither of them did the radiation treatment.
So in this day of medical research, we all have a much better chance of living to our 90s.
Jane