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e13094 Background: OS of pts with HR+ve/HER2-ve MBC has improved with CDK4/6i and endocrine therapy. Fulvestrant (FUL) works post progression on aromatase inhibitors in an endocrine resistant cohort. Ealcestrant (ELA) improves PFS compared to FUL in pts with an ESR1 mutation. This retrospective analysis looks at the trends in use of and associated outcome with FUL and ELA among pts with HR+ve/HER2-ve MBC. Methods: We utilized a federated network of de-identified health data representing approximately 135 million pt lives available through the TriNetX Research Network. We identified 14,387pts with HR+ve/HER2-ve MBC treated with endocrine therapy and CDK4/6i diagnosed between Nov 2018 - Nov 2023. OS was computed using the Kaplan Meier product limit method. Results: Mean age was 66 yrs. 5,736(39.9%) pts received FUL and 143(1%) pts ELA. In 2023 median time to use of FUL was 16m to 18m from metastases and median time to use of ELA decreased with time from 50m to 28m. Among pts who received ELA 65% received CDK4/6i for > 12m, 47% received FUL prior ELA, 7% received FUL after ELA. 5-yr OS of the whole cohort was 56.9%. 5-yr OS among pts who did and did not receive ELA was 85.4% and 60.0% respectively (HR 0.28, 95%CI 0.15-0.49, p 3m (HR 0.29, 95% CI 0.05-1.145, p=0.11). Among pts who received CDK4/6i > 12m 5-yr OS was 86.0% and 64.9% among pts who received ELA and FUL w/o ELA respectively (HR 0.36, 95% 0.20-0.67, p = 0.0007). Among pts who received ELA 1-yr OS from the start of ELA was 86.0% and 33.3% among pts who received CDK4/6i>12m and 12m. We continue to collect data among pts who are receiving ELA and expect over 200pts at the time of the presentation.
Dawood et al. (Sat,) studied this question.