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

Eligibility Criteria

• * Age ≥ 18 years.
• * Histological confirmation of primary breast cancer.
• * Patients with metastatic breast cancer and at least 12 months of clinical response to first-line systemic therapy, with the subsequent development of 1-3 extracranial sites of oligoprogressive disease, and who plan for the continuation of the current systemic therapy.
• * NOTE: patients with de novo metastatic disease and those developed metastatic disease after initially localized disease can both be included.
• * Patients with metastatic breast cancer and at least 6 months of clinical response to second-line systemic therapy (or further, e.g., third- or fourth-line), with the subsequent development of 1-3 extracranial sites of oligoprogressive disease.
• * ECOG Performance Status (PS) ≤ 2.
• * Negative urine or serum pregnancy test done ≤ 7 days prior to registration, for women of childbearing potential only.
• * Ability to complete questionnaire(s) by themselves or with assistance.
• * Provide written informed consent.
• * Willing to return to enrolling institution for follow-up (during the Active Monitoring Phase of the study).
• * Willing to provide blood samples for correlative research purposes.
• * Receiving radiation therapy as specified in the protocol.
• * Male patients.
• * Nursing or pregnant women.
• * Men or women of childbearing potential who are unwilling to employ adequate contraception.
• * Patients with triple negative disease (negative for ER, PR, and HER2).
• * Active second primary malignancy
• * \> 3 extracranial sites of oligoprogressive disease
• * Active CNS disease. Patients with asymptomatic and stable, treated CNS lesions (radiation and/or surgery and/or other CNS-directed therapy who have not received corticosteroids for at least 4 weeks) are allowed.
• * Active connective tissue disease that is felt by the treatment team to pose an excess risk of toxicity.
• * Prior radiation that overlaps with the intended treatment volume such that, in the opinion of the patient's Radiation Oncologist, radiotherapy to progressing sites will not be safe.
• * NOTE: patients with some dose overlap with prior radiotherapy that is deemed safe by the patient's Radiation Oncologist can be included in the trial.