So sorry to hear that.
My mother got breast cancer back in the early 90's. She had her breast removed and the chemo treatments and they said they got it all.
6 years ago it returned and quickly turned into stage 4. It is also in her bone (hip/leg), small spots in her liver and lungs (she never smoked).
Being too old for traditional chemo, they put her on Ibrance (chemo pill) and injections every 3 months. Just 2 months ago, they took her off
the Ibrance and started a new injection regiment of 2 shots every 2 weeks for 3 sessions, and now every 3 months.
Despite the stage 4 cancer, she has no pain and can get around without trouble. She lives alone and can still take care of herself and her finances.
She will be 96 in 2 weeks.
Wishing your wife all the best, and make sure you discuss all your treatment options that have become available with your Dr.