This study is a phase III multi-institutional randomized trial. Patients will be randomized in a 1:2 ratio between current standard of care treatment (Arm 1) vs. standard of care treatment + SABR (Arm 2) to sites of known disease.

Patients will be stratified by two of the strongest prognostic factors, based on a large multi-institutional analysis3: histology (Group 1: hormone-sensitive prostate cancer, breast, or renal; Group 2: all others), and number of metastases (Group 1: 1-3; Group 2: 4-10).

Inclusion Criteria:

• Age 18 years or older
• Willing to provide informed consent
• Karnofsky performance status > 60
• Life expectancy > 6 months
• Histologically confirmed malignancy with metastatic disease detected on imaging. Biopsy of metastasis is preferred, but not required.
• Total number of metastases 1-10 at the time of enrollment, with a primary tumor also present
• Restaging completed within 12 weeks prior to randomization (see section 5.1)
• For patients receiving thoracic radiotherapy, the enrolling physician must confirm there are no computed tomography (CT) changes suggestive of fibrotic interstitial lung disease (ILD) (i.e. reticular changes, traction bronchiectasis, or honeycombing) reported on any prior CT scans. If any are present, the patient must be assessed by a respirologist to rule out ILD prior to enrollment.
• 10 or fewer lifetime metastases from the cancer for which participants are being enrolled

Exclusion Criteria:

• Serious medical comorbidities precluding radiotherapy. These include ILD in patients requiring thoracic radiation, Crohn's disease in patients where the gastrointestinal (GI) tract will receive radiotherapy, or ulcerative colitis where the bowel will receive radiotherapy and connective tissue disorders such as lupus or scleroderma.
• For patients with liver metastases, moderate/severe liver dysfunction (Child Pugh B or C); please see the Child-Pugh score calculator.
• Substantial overlap with a previously treated radiation volume. Prior radiotherapy in general is allowed, as long as the composite plan meets dose constraints herein. For patients treated with radiation previously, biological effective dose calculations should be used to equate previous doses to the tolerance doses listed in Appendix 1. All such cases must be discussed with a member of the study steering committee.
• Malignant pleural effusion
• Inability to treat all sites of disease
• Brain metastasis > 3 cm in size or a total volume of brain metastases greater than 30 cc.
• Metastasis in the brainstem
• Clinical or radiologic evidence of spinal cord compression
• Metastatic disease that invades any of the following: GI tract (including esophagus, stomach, small or large bowel), or skin
• Pregnant or lactating women