ABSTRACT Scientific Rationale. Childhood cancer survivors (CCS) represent a vulnerable population at high risk of medical and psychosocial sequelae of cancer and cancer treatment necessitating survivorship care supported by Children’s Oncology Group (COG) long-term follow-up guidelines. However, current data indicate that most CCS are not receiving recommended survivorship care. To date, approaches to identify receipt of guideline- concordant care fail to routinely include community and organizational factors that may influence receipt of this care. There is a critical need to develop an approach to identify receipt of guideline-concordant care in real time, incorporating CCS-generated and community and organizational-level data to explore disparities in care and ultimately support future interventions targeting the sources of those disparities. Hypothesis. We hypothesize that development of an electronic health record (EHR)-based CCS registry supplemented with patient-generated data will (1) be feasible and acceptable to CCS, (2) provide actionable identification of CCS not receiving guideline-concordant care, and (3) enable assessment of community and organizational factors associated with receipt of guideline-concordant care. Project Design. In Aim 1, our multi-disciplinary research team will draft CCS data elements to incorporate into our existing EHR-based cancer registry system, Healthy Planet (Epic Systems™). We will emphasize data elements that are not traditionally part of EHR-registries including community (e.g., neighborhood social cohesion, Area Deprivation Index) and organization factors (e.g., availability/efficacy of pediatric-to-adult care transition visits for CCS, barriers to survivorship care plan development or access). A CCS Advisory Board (n = 6-10 adult CCS or parents of CCS <18 years of age) will then review the proposed data elements over the course of 2-3 Advisory Board meetings, driving iterative revision of registry elements. Aim 2 will recruit 30 adult CCS from the EHR-based registry to input patient-generated data into the registry including self-reported community-level data and patient perspectives on organizational-level factors. Feasibility will be assessed through participation rate and data completeness. Acceptability of CCS-generated data will be assessed via participant surveys. For Aim 3, we will compare assessments of guideline-concordant care between traditional retrospective chart review and the new EHR-based registry. We will conduct exploratory analyses to assess whether community and organizational factors explain disparities in receipt of guideline-concordant care. Next Steps. Development of the proposed EHR-based registry is a necessary, first step toward the design of cancer center-level interventions to eliminate disparities and improve CCS outcomes. Once sufficient data is available, we will perform definitive analyses to identify community and organization factors related to receipt of guideline-...