Abstract Background: Complex problems such as cancer disparities require deeper integration of social and scientific problem-solving and a broader systems approach. Given the nature of disparities, it also demands that we not just seek equitable outcomes but collaborate in ways that reflect equity in the process. To address breast and lung cancer disparities, we developed a unique transdisciplinary approach that creates teams inclusive of community, clinicians, and researchers and builds capacity to understand at a deep level the factors that underpin disparities and design and implement newer sustainable solutions. Methods: This study focuses on a phase I planning period for a transdisciplinary process with five teams locally embedded where lung and breast cancer disparities are significant. A leadership team that included primary investigators from academic medicine and public health supported community-based facilitators and evaluators responsible for guiding local teams. Deep equity, considerations on the biology to policy spectrum, and systems thinking are grounding principles in our approach. At the end of phase I, an evaluator facilitated After-Action Reviews (AAR) to assess effectiveness in maintaining fidelity to the framework and to identify successful practices and areas for improvement. These data informed changes to our approach to implementation to further root our commitment to equity during implementation. Seven AAR sessions were conducted: individual teams members, facilitators and evaluators, and the leaderships team (n-=50). The evaluator triangulated the data from the different AARs and facilitated a discussion of the integrated findings to the expanded leadership team. Results: The AAR highlighted three primary themes for critical self-reflection including (1) strengthening the understanding and use of our approach, (2) reducing ambiguity while preserving slack (e.g. flexibility with resources) and creativity, and (3) integrating project’s partners intentionally into our wider transdisciplinary network. In examining these themes, we identified several strategies for improving our transdisciplinary approach during implementation and for wider replication of our framework with future integrated science-social problem solving. These areas included improved systems for 360-degree communication, clear expectations of roles, and additional support for transdisciplinary collaboration and application of grounded principles to better self-organize a transdisciplinary system within a wider less resilient system like academic medicine. Discussion: To successfully innovate socially and scientifically within complexities of cancer disparities, we need to push beyond conventional models of research and program intervention. This means incorporating methods across fields and sectors including evaluation. An After-Action Review is an effective evaluation tool for assessing a complex process with numerous contributors to ensure a stronger outcome including more refined and relevant research questions and sustainability program, policy and practice. Citation Format: Tobi Cawthra, Laura Pinsoneault, Jerica Broeckling, Kristen Gardner-Volle, Tim Meister, Kailey Taebel, Jada Proctor, Felicia Fairfield, Kelly Hackett, David Frazer, Staci Young, Melinda Stolley. The Critical Role of Developmental Evaluation in Supporting and Enhancing an Equitable Transdisciplinary Approach to Address Cancer Disparities [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C011.