This is a randomized open-label multicentre Phase III superiority study of the effect of adding SBRT to the standard of care treatment on overall survival in patients with rare oligometastatic cancers. Patients will be randomized in a 1:1 ratio between current standard of care treatment vs. standard of care treatment + SBRT to all sites of known metastatic disease. The primary objective of this trial is to assess if the addition of stereotactic body radiotherapy (SBRT) to standard of care treatment improves overall survival (OS) as compared to standard of care treatment alone in patients with rare oligometastatic cancers.