Metastases-directed Radiotherapy in Addition to Standard Systemic Therapy in Patients With Oligometastatic Breast Cancer

Inclusion Criteria: * Metastasized breast cancer - up to 5 clinically manifest (new, progressive, persistent) metastases (a lymph node metastasis and a circumscribed local recurrence are each considered as one metastasis, i.e. also locoregional recurrent breast carcinomas with additional hematogenic metastasis possible) * maximum of 3 cerebral metastases known * indication for palliative drug therapy (endocrine therapy and/or chemotherapy and/or treatment with other substances) given according to guidelines (1st-line or further therapy lines, a special regime is not specified) * Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 2 * local radiation of all metastases possible * presentation of a written declaration of consent * patient ≥ 18 years Exclusion Criteria: * Previous radiotherapy, if this interferes with treatment within the scope of the study * symptomatic metastases requiring local therapy of all metastases (e.g. pain radiation), a radiation indication (or other local therapy) for individual metastases is not a criterion for exclusion * known central nervous system (CNS) metastasis without extracerebral metastasis (in these cases, immediate local therapy is mandatory) * more than three known CNS metastases (no indication for purely local therapy of only the metastases, primary whole brain radiation is indicated) * multifocal metastasis in one organ with impossibility to comply with the dose constraints for this organ (e.g., no indication for local th…