Abstract
Adolescents and young adults aged 15-39 years diagnosed with cancer are faced with unique challenges, which affect key developmental milestones and can create complex care needs. The aim of this study was to reach international consensus on the minimum set of outcomes to measure through the development of a core outcome set (COS). The COS development followed published methodological standards. A literature review and interviews with adolescents and young adults with cancer and health-care professionals generated a comprehensive list of 129 outcomes, spanning clinical and patient-reported outcomes relevant to adolescents and young adults with cancer. A three-round online Delphi survey involving three stakeholder groups globally, was implemented to reach international consensus. Overall, 262 respondents participated in the Delphi survey and 126 (48ยท1%) completed three survey rounds. 59 outcomes met consensus in round 3 and were taken forward to the consensus meeting. The final COS consists of 20 outcomes, including two on-treatment specific domains and three off-treatment specific domains. This study developed an adolescents and young adult-specific COS that, when implemented in clinical care and research, will improve the relevance of research findings, enhance care delivery, and enable consistent data synthesis across studies. Future efforts will focus on refining measurement methods and ensuring global applicability.