How would you treat an elderly female with metastatic HR+,HER2- breast cancer on endocrine therapy who now has progressive bone only disease?  

If it was minimal bone only progression, I would consider adding a CDK 4/6 to fulvestrant, albeit there is no data for doing so. I agree with checking for PI3K although I think this class of drugs is likely to be difficult to tolerate for someone described as elderly. Finally we still have the optio...

First, I would get a genomic profile looking for a PI3 kinase mutation, assuming she has good performance status and is a candidate for alpelisib. If she is truly endocrine resistant, then I would treat with capecitabine 2g/m2 on a one week one week off schedule. Finally, I would treat with zoledron...

There may also be a role for adding cdk 4/6 inhibitor therapy to current first line endocrine therapy. I agree with genetic profiling.