e23023 Background: Oncologic drug development is costly and protracted, often exceeding $2 billion USD and spanning over a decade. Window-of-Opportunity (WOO) clinical trials offer a novel, time-efficient approach for evaluating therapeutic strategies in treatment-naïve or recurrent cancer patients. Despite their potential, WOO trials face barriers such as low patient accrual and challenges associated with engaging early-stage cancer patients. We propose a structured patient partner (PP) model to enhance the design and execution of WOO trials, aimed at addressing accrual barriers and improving trial relevance and feasibility for trial participants. Methods: The Ontario Institute for Cancer Research (OICR) WOO Network implemented a five-step framework—acknowledge, appoint, apply, assess, and adjust—to facilitate meaningful PP engagement in WOO trials. This approach involved identifying and appointing PPs to specific trials aligned with their lived experience and expertise, providing comprehensive onboarding and training, and integrating their feedback into key trial components, including protocols, informed consent documents, and recruitment strategies. Patient engagement was evaluated annually over a three-year period (2022–2025) using the validated Patient Engagement in Research Scale (PEIRS-22). Results: Over three years, ten PPs contributed to nine WOO trials with 6, 7 and 6 PIERS assessments reported in 2022-2024 respectively. Each year, the PIERS feedback was used to determine refinements to improve the PP model. The median (IQR) overall engagement score was 87.5% (79.5%-95.5%), 85.2% (80.7%-97.7%) and 93.2% (79.8%-99.7%) by year respectively. Median scores across each of the 7 domains remained relatively constant across all three years, with the largest absolute improvement occurring in the general experience domain (22.5 to 25.5) and team environment domain (6.5 to 8.0), and no domain decreasing by more than 0.5 points. Conclusions: Meaningful engagement of PPs in clinical trials requires a deliberate, structured approach that integrates them at critical stages of the trial lifecycle, combined with robust evaluation mechanisms to identify areas for improvement to drive continuous refinement. Future efforts will prioritize careful evaluation of the impact of successful PP engagement on improving trial accrual outcomes.