Reusing clinical trial data to consolidate and advance medical knowledge.

While data sharing holds great potential to maximize the value of research and reduce waste, these benefits can only be fully realized if shared data are also effectively reused. Yet, data reuse remains limited, and there is a notable lack of clear guidelines to support data reusers. Reusing existing data enables a wide range of valuable activities, including validating previous findings, identifying errors, conducting individual patient data meta-analyses, performing secondary analyses, and developing or testing new methods. However, the validity of such work depends on strict adherence to reproducible research practices-arguably even more so in the context of secondary use. Data reuse also involves practical constraints and specific challenges, such as addressing feasibility issues, which must be anticipated and managed from the outset. Researchers should remain aware of these considerations throughout the entire lifecycle of a reuse study. Ideally, this process should be supported by hands-on training tailored to the specific demands of data reuse. To that end, we propose a set of guiding principles to foster responsible and meaningful reuse of existing datasets-including, but not limited to, assembling a skilled multidisciplinary team, anticipating infrastructure and interoperability challenges, maintaining transparency throughout the research process, and incentivizing all stakeholders involved.