Detailed positive results from the head-to-head DESTINY-Breast03 Phase III trial showed that Enhertu (trastuzumab deruxtecan), the AstraZeneca and Daiichi Sankyo Company, Limited (hereafter, Daiichi Sankyo) HER2-directed antibody drug conjugate (ADC), demonstrated superior progression-free survival (PFS) versus trastuzumab emtansine (T-DM1), a HER2-directed ADC currently approved to treat patients with HER2-positive unresectable and/or metastatic breast cancer previously treated with trastuzumab and a taxane. Results were presented today in a Presidential Symposium at the European Society for Medical Oncology (ESMO) Congress 2021.
At a prespecified interim analysis of DESTINY-Breast03, Enhertu demonstrated a 72% reduction in the risk of disease progression or death compared to T-DM1 (hazard ratio [HR] 0.28; 95% confidence interval [CI] 0.22-0.37; p=7.8×10-22). After 15.5 and 13.9 months of follow-up in the Enhertu and T-DM1 arms respectively, the median PFS for patients treated with Enhertu was not reached (95% CI 18.5-NE) compared to 6.8 months for T-DM1 (95% CI 5.6-8.2) as assessed by blinded independent central review (BICR).
In the key secondary endpoint of PFS assessed by investigators, patients treated with Enhertu experienced a three-fold improvement in PFS of 25.1 months versus 7.2 months for T-DM1 (HR 0.26; 95% CI 0.20-0.35; p=6.5×10-24). A consistent PFS benefit was observed in key subgroups of patients treated with Enhertu, including those with a history of stable brain metastases.
There was a strong trend towards improved overall survival (OS) with Enhertu (HR 0.56; 95% CI 0.36-0.86; nominal p=0.007172), however this analysis is not yet mature and is not statistically significant. Nearly all patients treated with Enhertu were alive at one year (94.1%) compared to 85.9% of patients treated with T-DM1.
Confirmed objective response rate (ORR) more than doubled in the Enhertu arm versus the T-DM1 arm (79.7% vs. 34.2%). Forty-two (16.1%) complete responses (CR), and 166 (63.6%) partial responses (PR) were observed in patients treated with Enhertu compared to 23 (8.7%) CRs and 67 (25.5%) PRs in patients treated with T-DM1.
Javier Cortés, MD, PhD, Head, International Breast Cancer Center (IBCC), Barcelona, said: “Patients with previously treated HER2-positive metastatic breast cancer will typically experience disease progression in less than a year with available HER2-directed treatments. The high and consistent benefit seen across efficacy endpoints and key subgroups of patients receiving Enhertu in DESTINY-Breast03 is remarkable and supports the potential of Enhertu to become the new standard of care for those who have previously been treated for HER2-positive metastatic breast cancer.”
Susan Galbraith, Executive Vice President, Oncology R&D, said: “Today’s results are ground-breaking. Enhertu tripled progression-free survival as assessed by investigators, and provided a disease control rate exceeding 95% compared to 77% for T-DM1 in DESTINY-Breast03. In addition, the safety profile was encouraging with no Grade 4 or 5 interstitial lung disease events in this trial. These unprecedented data represent a potential paradigm shift in the treatment of HER2-positive metastatic breast cancer, and illustrate the potential for Enhertu to transform more patient lives in earlier treatment settings.”
Ken Takeshita, Global Head, R&D, Daiichi Sankyo, said: “The early survival data, which evaluated Enhertu against another HER2-directed ADC, showed that nearly all patients treated with Enhertu were alive after a year and is a positive indication of the potential of this medicine to transform the treatment of HER2-positive metastatic breast cancer. These landmark data will form the basis of our discussions with global health authorities to potentially bring Enhertu to patients with previously treated HER2-positive metastatic breast cancer as a more effective treatment option as soon as possible.”
Summary of results: DESTINY-Breast03