Trastuzumab deruxtecan in previously treated patients with HER2-positive metastatic breast cancer: updated survival results from a phase II trial (DESTINY-Breast01)

Background: Primary analysis of the multicenter, open-label, single-arm, phase II DESTINY-Breast01 trial (median follow-up 11.1 months) demonstrated durable antitumor activity with trastuzumab deruxtecan (T-DXd) in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (mBC) previously treated with trastuzumab emtansine (T-DM1). We report updated cumulative survival outcomes with a median follow-up of 26.5 months (data cut-off 26 March 2021).

Patients and methods: Patients with HER2-positive mBC resistant or refractory to T-DM1 received T-DXd 5.4 mg/kg intravenously every 3 weeks until disease progression, unacceptable adverse events, or withdrawal of consent. The primary endpoint was confirmed objective response rate (ORR) by independent central review (ICR). Secondary endpoints included overall survival (OS), duration of response (DoR), progression-free survival (PFS), and safety.

Results: The ORR by ICR was 62.0% [95% confidence interval (CI) 54.5% to 69.0%] in patients who received T-DXd 5.4 mg/kg every 3 weeks (n = 184). Median OS was 29.1 months (95% CI 24.6-36.1 months). Median PFS and DoR were 19.4 months (95% CI 14.1-25.0 months) and 18.2 months (95% CI 15.0 months-not evaluable), respectively. Drug-related treatment-emergent adverse events (TEAEs) were observed in 183 patients (99.5%), and 99 patients (53.8%) had one or more grade ≥3 TEAEs. Adjudicated drug-related interstitial lung disease/pneumonitis occurred in 15.8% of patients (n = 29), of which 2.7% (n = 5) were grade 5.

Conclusions: These updated results provide further evidence of sustained antitumor activity of T-DXd with a consistent safety profile in heavily pretreated patients with HER2-positive mBC.