Abstract

5601 Background: Over the past decade, progress has been made in treating aEC, with newer therapies introduced in the first-line (1L) and second-line (2L) setting. Molecular profiling of MMR/MSI has emerged as a valuable tool for guiding treatment decisions, but real-world evidence on the shifting treatment paradigm is limited. Thus, this study aims to assess molecular profiling uptake, treatment patterns, and outcomes among aEC pts. Methods: This retrospective study included pts from the nationwide Flatiron Health electronic health record-derived deidentified database who were diagnosed with aEC (stage III/IV or recurrent) and initiated 1L therapy between 1/1/2018 and 6/30/2023. Patient characteristics, treatment patterns, and real-world time to next treatment (rwTTNT) were examined across MMR/MSI status: deficient (dMMR), proficient (pMMR), and never tested (NT). Kaplan-Meier methods were used to generate unadjusted time to event estimates. Results: A total of 1,441 pts met study criteria. Median age at aEC diagnosis was 68 years (range: 26-85), 1,056 (73%) were treated in the community setting, and 1,199 (83%) received MMR/MSI testing. Endometrioid carcinoma occurred in 619 (43%) overall and was the predominant histology (231/293; 79%) in dMMR. Approximately 15% had record of another cancer diagnosis at any point. NT pts were more likely than those tested to be Black or African American (26% vs 18%) and diagnosed with stage IV disease (55% vs 48%). The table presents select therapies and rwTTNT estimates. pMMR pts often received platinum-based chemotherapy (PBCtx) in 1L (67%) and immune checkpoint inhibitor (CPI) + vascular endothelial growth factor (VEGF) inhibitor therapies in 2L (23%), while dMMR pts were more likely than others to receive other CPI regimens (mono, combo + chemo) in 1L (23%) and 2L (44%). Median rwTTNT was similar across subgroups in 1L but was markedly longer among dMMR pts (10.8 vs 5-6 months) in 2L. Conclusions: While MMR/MSI testing was common, use of 2L immunotherapy for dMMR (51%) and CPI + VEGF for pMMR (23%) was lower than expected and may reflect slow uptake of recently approved, molecular profile-specific therapies. MMR/MSI testing gaps remain, especially in underrepresented pts, and may be a barrier to adoption of new therapies. Future analyses will be critical to assess changes in outcomes over a longer timeframe. Continued education is needed to increase access to newer FDA approved treatments. [Table: see text]