Background: This is a randomized Phase II trial to evaluate if stereotactic body radiotherapy (SBRT) and/or surgical resection (SR) of all metastatic sites in oligo-metastatic breast cancer who have received up to 6 months of first line systemic therapy without progression will significantly improve median progression free survival (PFS). If this aim is met the trial continues as a phase III to evaluate if SBRT/SR improves 5 year overall survival (OS). Secondary aims include local control in the metastatic site, distant metastatic rate, and technical quality. Translational primary endpoint is to determine whether < 5 CTCs is an independent prognostic marker for improved PFS and OS. Predictive value of CTCs will be assessed. Methods: Women with pathologically confirmed metastatic breast cancer to < / = 2 sites who have received up to 6 months of standard first line systemic therapy and the primary site disease is controlled are eligible. CNS metastases are ineligible. ER/PR and HER-2 neu is required on the primary or metastatic site. Site radiation credentialing with a facility questionnaire and a case benchmark is required. Randomization is to local radiotherapy/ surgery for palliation only when necessary versus ablation of all metastases with SBRT and/or SR. Statistics: For the phase IIR portion to detect a signal for improved median PFS from 10.5 to 19 months with 95% power and accounting for ineligible/lost patients, 146 patients will be required. For the Phase III, an additional 246 patients will be required to definitively determine if ablative therapy improves 5-year OS from 28% to 42.5% (HR = 0.67), with 85% power and a one-sided type I error of 0.025. For the translational research, the number of patients accrued in Phase IIR and Phase III portions will provide sufficient power of at least 91% to detect whether < 5 CTC’s is a prognostic marker for improved PFS and OS. Contact Information: Protocol: CTSU member web site https://www.ctsu.org. Pt enrollment: OPEN at https://open.ctsu.orgor the OPEN tab on CTSU member web site. Support: NCI U10CA180868 and U10CA180822 Clinical trial information: Pending.