Among patients with breast cancer the subgroup of patients with metastases are considered the group of patients with the worst prognosis. Not only regard-ing therapy decisions but also with regard to quality assured healthcare and health economics this entity of patients remains a challenge. Recently, novel advances in breast cancer therapy aim at the targeted therapy of tumor entities and identification of patients, for whom the greatest therapy benefit, and the least side effects are expected. However molecular assessment of the patient and the tumor in the metastatic situation is not performed on a routine basis and in many cases tumor character-istics from the primary tumor are considered reliable enough to make therapy decisions for the metastatic patients. Although molecular reassessment of tu-mor characteristics from tumor material of the metastasis is recommended in national guidelines, only a minority of patients is biopsied, because of the inva-siveness of the procedure, even though biopsy related complications are reported to be rare. With modern analytic methods from blood based biomaterial there seems to be an opportunity to correlate blood based tumor assessments with actual charac-teristics of the tumor. These include expression analysis, tumor mutation analy-sis, tumor gene copy number aberrations and others. One of the main aims of the PRAEGNANT study is therefore to establish an infrastructure for the compre-hensive analysis of tumor and metastatic molecular characteristics of the patient and the tumor. Furthermore, health care related outcomes as well as health economics provide novel approaches for integration of patients in study conduct and health care awareness and are study aims of the PRAEGNANT study.