Stereotactic Body Radiotherapy in Patients With Rare Oligometastatic Cancers (OligoRARE)

Inclusion Criteria: * Histologically confirmed malignancy with metastatic disease detected on imaging. Biopsy of metastasis is preferred, but not required. * Controlled primary tumour, defined as: * at least 3 months since original tumour treated definitively, with no progression at primary site * Total number of oligometastases of 1-5 including: * Brain metastases amenable to radiosurgery or fractionated stereotactic radiotherapy patient who had neurosurgical resection before trial inclusion are allowed and resected brain metastases count to the total number of oligometastases * All sites of disease can be safely treated based on the judgement of an experienced radiation oncologist * ECOG score 0-2 * Life expectancy \> 6 months * Age 18 or older * Before patient randomization, written informed consent must be given according to ICH/GCP, and national/local regulations. Exclusion Criteria: * Primary cancer of prostate, breast, lung or colorectal * Serious medical comorbidities precluding radiotherapy: * These include interstitial lung disease in patients requiring thoracic radiation, Crohn's disease in patients where the 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) * 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 previously with radiation, biological effective dose calculations should be used to equate previous doses to the tolerance doses listed in the RTQA Guidelines. All such cases should be discussed with one of the study coordinators * Brain metastases only, without extra-cerebral metastases * Malignant pleural effusion, malignant ascites, meningeal carcinomatosis and peritoneal carcinomatosis * Maximum size of 6 cm for lesions outside the brain, except: * Bone metastases over 5 cm may be included, if in the opinion of the local radiation oncologist it can be treated safely (e.g. rib, scapula, pelvis) * Clinical or radiologic evidence of symptomatic spinal cord compression. Patients can be eligible if surgical resection has been performed, but the surgical site counts toward the total of up to 3 metastases. * Metastatic disease that invades any of the following: GI tract (including oesophagus, stomach, small or large bowel), mesenteric lymph nodes, or disseminated skin metastases and lymphangiosis * Pregnant or breast feeding women * Any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with the patient before randomization in the trial