ABSTRACT

Background: Most of the published data with trastuzumab deruxtecan (T-DXd) derive from clinical trials with selected populations and little representation of US patients. Limited real-world data are available.
Patients and methods: Using a nationwide electronic health record-derived database, we identified patients with metastatic breast cancer (MBC) who initiated T-DXd between December 2019 and September 2023. Tumors were categorized as human epidermal growth factor receptor 2 (HER2)-positive if positive at any time before starting T-DXd and HER2-negative if never HER2-positive before T-DXd. Hormone receptor (HR) status was derived from the last biopsy before T-DXd initiation. Real-world progression-free survival (rwPFS) and overall survival (OS) were estimated using the KaplaneMeier method.
Results: Overall, 1490 patients were included: 884 with HER2-positive, 487 with HR-positive/HER2-negative, and 119 with HR-negative/HER2-negative (triple-negative) MBC. Median age was 59 years (range 23-84 years), and median prior lines of systemic treatments were 3 and 4 for HER2-positive and HER2-negative MBC, respectively. rwPFS and OS were 12.3 and 24.6 months for HER2-positive disease; 7.6 and 15.5 months for HR-positive/HER2-negative disease; and 4.3 and 10.4 months for triple-negative disease. T-DXd use in earlier lines of treatment was associated with significantly longer rwPFS in HER2-positive (P ¼ 0.02), but not in HR-positive/HER2-negative MBC (P ¼ 0.07).
Among patients with triple-negative disease pretreated with sacituzumab govitecan (SG, n ¼ 58), after
adjusting for prior lines of treatment, shorter rwPFS (3.4 versus 5.7 months, P ¼ 0.009) and OS (9.0 versus 14.5 months, P ¼ 0.002) were observed compared with patients without prior SG (n ¼ 61). rwPFS with T-DXd was also significantly shorter in patients with BRCA mutations (7.8 versus 9.2 months, P ¼ 0.02) and numerically shorter in patients with programmed death-ligand 1-negative disease (6.9 versus 12.6 months, P ¼ 0.31).
Conclusions: In a large dataset, T-DXd showed favorable activity for treating MBC, although outcomes for HER2-positive disease appeared worse than those observed in clinical trials. Prior SG treatment was associated with inferior outcomes with T-DXd, suggesting cross-resistance between these antibodyedrug conjugates.