Background <p>In Germany, approximately one in eight women will be diagnosed with breast cancer during their lifetime, making it the most prevalent form of cancer among women and the leading cause of cancer-related mortality worldwide. Metastatic breast cancer is associated with substantial morbidity and a&#xa0;diminished quality of life (QoL). The primary therapeutic objective in this setting is to prolong survival while preserving the best possible QoL.</p> Objective <p>The PRO&#xa0;B trial aimed to improve care for patients with advanced disease through digitally supported symptom monitoring. Patient-reported outcomes (PROs) were employed to systematically capture and quantify patient-reported symptoms and QoL metrics in order to facilitate early detection of disease- or treatment-related adverse effects and timely clinical intervention.</p> Methods <p>The PRO&#xa0;B study was a&#xa0;multicenter randomized controlled trial conducted across 52&#xa0;breast cancer centers in Germany enrolling 924&#xa0;patients with metastatic breast cancer undergoing systemic antineoplastic therapy. Participants in the intervention arm completed weekly digital PRO assessments via a&#xa0;mobile application. These PRO data were made accessible to the clinical care team through a&#xa0;web-based portal, which generated automated alerts in response to clinically significant deteriorations in PRO scores.</p> Results <p>The results show that an alarm-based PRO monitoring system can be implemented in patients with metastatic breast cancer and is well received, not only in university hospitals with particularly high case numbers but also in breast cancer centers of different sizes, sponsorship, and research activity.</p> Conclusion <p>The PRO&#xa0;B study is the first to demonstrate successful implementation of clinically relevant PRO monitoring for patients with metastatic breast cancer in routine care across the German healthcare system. The potential of this model of care should also be evaluated for other oncological diseases.</p>