Impact of use of antibody drug conjugates on the prognostic outcome of patients with HR+ve/HER2-ve MBC: Results from a real world dataset.

1076 Background: Two antibody drug conjugates trastuzumab deruxtecan (T-DXd - in the HER2 low cohort) and sacituzumab govitecan (SG) have been shown to improve both PFS and OS among pts with HER-ve MBC. The objective of this retrospective analysis was to look at trends in the use of and associated prognostic outcome associated with T-DXd and SG among pts with HR+ve/HER2-ve MBC in the real-world setting. Methods: We utilized a federated network of de-identified health data representing approximately 107 million pt lives available through the TriNetX Research Network. We identified pts with HR+ve/HER2-ve MBC diagnosed between Jan 2004 and Jan 2024. Propensity score matching analysis by age, site of metastases and chemotherapy was carried. OS was computed using the Kaplan Meier product limit method. Results: 17,133 pts with HR+ve/HER2-ve MBC treated with endocrine therapy and CDK4/6i were identified of whom 249 pts (1.45%) and 162 pts (0.94%) received SG and T-DXd respectively. 32 pts (0.19%) received T-DXd + SG. Median time from diagnosis of MBC to start of SG and T-DXd was 625 days and 233 days respectively. 5-yr OS for the whole cohort was 58.1%. 5-yr OS among pts who did and did not receive T-DXd was 74.8% and 52.2% respectively (HR 0.44, 95% CI 0.28 - 0.69; p = 0.0002). 5-yr OS among pts who did and did not receive SG was 73.4% and 64.7% respectively (HR 0.62 95% CI 0.42 - 0.90, p=0.012). 5-yr OS among pts who did and did not receive T-DXd + SG was 77.4% and 62.4% respectively (HR 0.55, 95% CI 0.19 - 1.59, p=0.26). 5-yr OS was 68.1% and 74.5% among pts who had received SG alone or T-DXd alone respectively (HR 1.31, 95% CI 0.84 - 2.03, p =0.22). Conclusions: In a real-world data set we report on the OS benefit associated with the use of SG and/or T-DXd at some time point in the therapy of pts with HR+ve/HER2-ve breast cancer who have progressed on endocrine therapy and CDK4/6i.