My late first wife lived 7 years after her Stage 4 BC diagnosis, and it was found rather late as Stage 4s go, so well-advanced. In her case the tumors were ER positive, so she spent a lot of time on estrogen blockers and alternated that every now and then with traditional chemo. Which could also be done rather gently. Plus spot radiation now and again on the few tumors sited where radiation was relevant.
There are many, many new and better estrogen blockers than the traditional tamoxifen which is pretty much a hormonal sledgehammer. Wife found most of those easy to take, unlike tamoxifen that gave her fits.
Breast cancer preferentially metastasizes to brain, bone, lungs, and liver. By the time my wife was done, she had had all 4. But bone was the first to be affected, and it’s a good bet an x-ray or CT saw something suspicious on your friend’s humerus that they want to know more about. Hence the biopsy.
By unhappy coincidence, today would have been her 68th birthday had she lived. I hope her memory plus my vague recollections and detailed notes of her long and varied treatment history can assist your friend somehow.