The purpose of this study is to see if using Stereotactic Body Radiation Therapy/SBRT to treat a single metastatic site where cancer has worsened may be an effective treatment for people with oligometastatic breast cancer. Participants will stay on their usual drug therapy while they receive SBRT. This combination of SBRT to a single metastatic site and usual drug therapy may prevent participants' cancer from worsening in other metastatic sites or spreading.
Age 18 or older
Willing and able to provide informed consent
Metastatic breast cancer, biopsy proven
ER+/HER2-, defined as >5% ER+ staining
Pregnancy
Serious medical comorbidity precluding radiation, including connective tissue disorders
Intracranial disease (including previous intracranial involvement)
Previous radiotherapy to the intended treatment site that precludes developing a treatment plan that respects normal tissue tolerances.