Understanding return to work after breast cancer through real-world data linkage framework: a Luxembourg digital oncology use case.

Background: Breast cancer (BC) has a substantial impact on women of working age, making return to work (RTW) a critical outcome to evaluate. Research on RTW relies on individual-level real-world data integrating clinical and occupational information. Luxembourg offers a unique setting for such studies, with a young population and a high number of crossborder workers, creating specific challenges and opportunities for studying RTW. This study aims to describe a secure data linkage framework integrating population-based cancer registry, occupational health records, and questionnaire data to evaluate RTW after BC in Luxembourg. Materials and methods: A cross-sectional pilot study was conducted linking data from three sources: from Luxembourg's National Cancer Registry (RNC), occupational health records from the Service de Santé au Travail Multisectoriel (STM), and results from a 27-item self-administered questionnaire. Eligible women were diagnosed with BC between 2013 and 2018, were younger than 65 years, employed under Luxembourgish labour law, and followed by STM. Potential participants were identified through STM records and invited to complete an electronic questionnaire and provide explicit consent for data linkage via REDCap® (Research Electronic Data Capture). A deterministic linkage between RNC and STM was enabled by using a common pseudonymisation service. Sociodemographic, clinical, and work-related characteristics were compared between linked and nonlinked participants and between women who did and did not RTW. Results: Among 452 women contacted, 171 completed the questionnaire and provided informed consent (38% response rate). Ninety-six were successfully linked with the RNC dataset. Having Luxembourg as nationality or country of residence was associated with successful linkage ( Conclusions: Pseudonymised deterministic data linkage across three real-world data sources, including population-based cancer registry data, is feasible, and provides unique insights into RTW after BC. Crossborder residency patterns and heterogeneous cancer definitions between sources were key barriers to complete linkage. The population-based approach enables a more complete picture of RTW trajectories among women with BC, supporting robust real-world evidence and informing RTW surveillance and occupational health policies in highly mobile European crossborder regions.