How would you treat a patient with ER/PR positive breast cancer with a single site of bone metastasis?

I would still treat with hormone therapy and a CDK 4/6 inhibitor. Not clear if the question refers to denovo disease or not. I generally do not treat asymptomatic bone mets with radiation, as there are late effects in patients who have a relatively long life expectancy and no data to suggest that radiating a single site will improve survival. If we are combining immunotherapy in the future that might change! For denovo disease it very much depends on tumor biology and extent of local disease as well as age. In general I would use a hormone based approach, although I would be sure to document by biopsy the focus of metastatic disease.