Primary Breast Oligoprogressive Sites Treated With Radiotherapy to Obviate the Need to Change Systemic Therapy

This study is testing whether targeted radiation therapy to a small number of tumor spots that have started growing again (called oligoprogression) can delay the need to switch to a new systemic therapy (like chemotherapy or hormone therapy) in people with metastatic breast cancer. **You may be eligible if...** - You have been diagnosed with metastatic breast cancer - You responded well to your current systemic therapy for at least 12 months (first-line) or 6 months (second-line or later), and now only 1–3 spots outside the brain have started growing - You plan to continue your current systemic treatment - Your general health is good (ECOG 0–1) **You may NOT be eligible if...** - You have brain metastases that are progressing - You have more than 3 sites of new tumor growth - You are pregnant or breastfeeding - You have had prior radiation that would overlap with the planned treatment areas Talk to your doctor to see if this trial is right for you.