FDG-PET/CT vs. CT for Monitoring Metastatic Breast Cancer

Several studies have shown improved sensitivity of FDG-PET/CT compared with conventional imaging for diagnosing metastatic breast cancer in retrospective and smaller prospective studies. For response monitoring, we expect FDG-PET/CT to detect disease progression earlier than CT in patients treated for metastatic breast cancer, enabling earlier start of second-line therapies. Current knowledge about the potential benefit of FDG-PET/CT for response monitoring of patients with metastatic breast cancer comes from observational studies. Consequently, current evidence is only hypothesis-generating and prospective, randomized trials such as the MONITOR-RCT are needed to corroborate these findings. The MONITOR-RCT clinical trial aims to investigate whether monitoring with FDG-PET/CT can improve survival in patients diagnosed with metastatic breast cancer. It is a parallel group comparative randomized trial comparing an experimental monitoring strategy based on FDG-PET/CT with a standard monitoring strategy based on CT. Participating patients should have newly diagnosed metastatic breast cancer and be considered eligible for initiating first-line medical treatment and subsequent regular response monitoring. A total of 420 patients will be included in the study, with recruitment taking place across 11 participating hospital sites in Denmark, Germany, and Italy. The main questions it aims to answer are: * Can monitoring with FDG-PET/CT compared to conventional CT prolong the overall survival of MBC patients? * Is this-as expected-due to earlier detection of disease progression and earlier initiation of second-line therapies? * Is this accompanied by less need for additional diagnostics, less need for hospitalization, and improved quality of life? Participants will: * Undergo FDG-PET/CT scans at scheduled intervals to monitor disease progression. * Be given standard treatments as part of oncological care, which is informed by the FDG-PET/CT scans * Fill out questionnaires about their quality of life at various time points throughout the study. Objectives are: Primary: To demonstrate superiority in overall survival of response monitoring with FDG-PET/CT in patients with metastatic breast cancer over response monitoring based on CT. Appropriately adapted PERCIST criteria for FDG-PET/CT and the RECIST1.1 criteria for CT will be used. Secondary: To demonstrate superiority in quality of life and exposure to oncologic treatment with FDG-PET/CT and to investigate the cost-effectiveness.