CORE is a phase II/III, multi-centre, non-blinded, parallel group randomised controlled trial in patients with breast, prostate or NSCLC primary cancer comparing standard of care (SOC) with or without SBRT for extra-cranial metastases. The aim of the phase II study is to demonstrate 1) feasibility of recruitment, 2) deliverability of the study in a multi-centre setting and 3) activity of SBRT, based on progression free survival, across the three tumour types. If all three aims are achieved the trial will be amended to roll into parallel tumour-site specific phase III trials.