(P 450) OUTCOMES IN CLEAR CELL SARCOMA: UPDATED INSIGHTS FROM ELECTRONIC HEALTH RECORDS IN A PATIENT-LED REGISTRY

Objective: Clear Cell Sarcoma (CCS) is a rare, aggressive soft tissue sarcoma driven by EWSR1-ATF1 gene fusion. It typically affects adolescents and young adults and is known for its resistance to conventional therapies and tendency to metastasize early. Clinical trial data are extremely limited due to its ultra-rare nature. To address this gap, we previously reported early findings from a patient-led registry utilizing de-identified electronic health records (EHRs) to help characterize the natural history of CCS. The objective of this study is to present updated analyses from this registry, reflecting expanded enrollment and additional real-world outcome data.

Methods: Patients or caregivers contributed de-identified EHRs through a secure data collection platform. Records were reviewed and curated by a trained medical data team. Extracted data included demographic information, tumor location and stage, treatment history (surgery, radiation, systemic therapy), progression events, and survival outcomes. Each included case had a confirmed Diagnosis of CCS with EWSR1-ATF1 gene fusion documented in the EHR. Descriptive statistics were used to summarize clinical characteristics and treatment patterns, with subgroup comparisons where applicable.

Results: As of June 2025, the registry includes 22 CCS patients, with ongoing data analysis underway. Preliminary trends in treatment patterns, disease progression, and clinical outcomes are being evaluated. Final results will be available at the time of presentation.

Conclusion: This expanded dataset reinforces the feasibility and value of patient-led EHR registries in rare cancers. Real-world data collection enables deeper insight into treatment patterns and outcomes, offering an essential bridge while prospective clinical trials remain limited in CCS. Ongoing updates will further inform clinical decision-making and research priorities.