It is difficult to quantify incidence of patients with multiple primary cancers developing at intervals that are representative of oligometastatic stage IV disease, (defined for the purposes of this trial as ≤ 3 metastatic sites). However an increase in the use of surveillance imaging, together with improved diagnostic sensitivity has led to the diagnosis of patients with asymptomatic oligometastatic relapse becoming a more common clinical occurrence. The CORE study is a randomized controlled trial that will be conducted in patients with cancer in one of three primary sites where oligometastatic disease relapse is a common clinical scenario: breast, prostate and non-small cell lung cancer (NSCLC). The study will evaluate the use of SBRT in this patient population.