Abstract PS5-02-03: Clinical Outcomes of Trastuzumab Emtansine (T-DM1) Following Trastuzumab Deruxtecan (T-DXd) in Metastatic Breast Cancer: A Single-Center Experience

Abstract Background: HER2-positive metastatic breast cancer (MBC) remains an oncological challenge afterdisease progression to pertuzumab-trastuzumab, and fam-trastuzumab deruxtecan. Data on treatmentoutcomes with T-DM1 following progression on trastuzumab deruxtecan (T-DXd) remain limited. This study evaluates the clinical outcomes of patients with HER2-positive MBC who received T-DM1 post-T-DXd. Methods: Demographics and clinical characteristics were summarized for the whole cohort who received T-DM1 after T-DXd. Continuous variables were summarized using medians and ranges, while categorical variables were summarized using frequencies and percentages. Overall survival (OS), defined as the time from the date of receiving T-DM1 to the date of death or last follow-up, progression-free survival (PFS),defined as the time from the date of receiving T-DM1 to the date of first documented disease progression or death, whichever occurred first, and time to progression (TTP), defined as the time from the date of receiving T-DM1 to the date of disease progression, were evaluated using the Kaplan-Meier method, and differences in survival curves were compared using the log-rank test. Cox proportional hazards regression models assessed associations between survival outcomes and clinical variables. The overall response rate was calculated based on the proportion of patients experiencing progressive or stable disease. A p-value