Inclusion Criteria:

• Pathologically confirmed metastatic breast cancer within 270 days prior to registration.
• Known estrogen, progesterone, and HER2 status of either primary tumor or metastasis.
• ≤ 2 metastases seen on standard imaging within 30 days prior to registration.
• Controlled primary tumor site defined as ≥ 3 months (90 days) recurrence-free interval since completion of definitive surgical management.
• All known disease amenable to metastasis-directed therapy with either SBRT or resection:
  • Symptomatic bone metastasis allowed if ablative therapy can be delivered;
  • Sites for possible surgical excision include lung, liver, adrenal gland, bone, small intestine, large intestine, ovary, and amenable nodal disease sites;
  • Surgical stabilization is allowed for a metastasis if it is followed by conventionally fractionated external beam radiotherapy.
• Maximum diameter of individual metastasis in any dimension ≤ 5 cm.
• Metastases must be > 5 cm away from each other (defined as Edge to Edge of tumor):
  • If metastases are ≤ 5 cm away from each other, consider enrollment in NRG-BR001.
• First-line standard systemic therapy (chemotherapy, anti-endocrine therapy, anti-HER2 or other standard targeted therapy) for metastatic breast cancer not to have exceeded a duration of 6 months at the time of registration.
• Appropriate stage for study entry based on the following diagnostic workup:
  • History/physical examination within 30 days prior to registration;
  • Computed tomography (CT) scans of the chest, abdomen, and pelvis with radionuclide bone scan or whole body positron emission tomography (PET)/CT within 30 days prior to study registration.
• Zubrod performance status ≤ 2 within 30 days prior to registration.
• Absolute neutrophil count (ANC) ≥ 500 cells/mm^3.
• Platelets ≥ 50,000 cells/mm^3.
• Hemoglobin ≥ 8.0 g/dl: 
  • The use of transfusion or other intervention to achieve hemoglobin [Hgb] ≥ 8.0 g/dl is acceptable.
• For females of child-bearing potential, negative serum or urine pregnancy test within 14 days prior to study registration.
• Must provide study-specific informed consent prior to study entry.

Exclusion Criteria:

• Pathologic evidence of local/regional breast tumor recurrence.
• Co-existing or prior invasive malignancy (except non-melanomatous skin cancer), unless disease free for a minimum of 3 years.
• Metastases with indistinct borders making targeting not feasible:
  • Potential issue with bone metastases that they often are not discrete;
  • Since many on this protocol will have bone metastases, this will be an important issue;
  • Theoretically, Houndsfield units might provide an appropriate measure, however, a sclerotic lesion against dense cortical bone will not have a sharp demarcation based on Houndsfield units;
  • It is acknowledged that such determinations will pose a challenge and the physician's judgment will be required.
• Prior palliative radiation treatment for metastatic disease.
• Metastases located within 3 cm of the previously irradiated structures:
  • Spinal cord previously irradiated to > 40 Gy;
  • Brachial plexus previously irradiated to > 50 Gy;
  • Small intestine, large intestine, or stomach previously irradiated to > 45 Gy;
  • Brainstem previously irradiated to > 50 Gy;
  • Lung previously irradiated with prior V20Gy > 30%.
• Brain metastases.
• Exudative, bloody, or cytological proven malignant effusions.
• Severe, active co-morbidity defined as follows:
  • Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months;
  • Transmural myocardial infarction within the last 6 months;
  • Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration;
  • Chronic obstructive pulmonary disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy at the time of registration.
• Pregnancy.
• Lactating females must cease expression of milk prior to signing consent.
• Human immunodeficiency virus (HIV) positive with cluster of differentiation (CD)4 count < 200 cells/microliter:
  • HIV positive is eligible, provided is under treatment with highly active antiretroviral therapy (HAART) and has a CD4 count ≥ 200 cells/microliter within 30 days prior to registration;
  • HIV testing is not required for eligibility.