Positive results from the DESTINY-Breast09 Phase III trial showed Enhertu (trastuzumab deruxtecan) plus pertuzumab demonstrated a highly statistically significant and clinically meaningful improvement in progression-free survival (PFS) compared to a taxane, trastuzumab and pertuzumab (THP) as a 1st-line treatment for patients with HER2-positive metastatic breast cancer.
Results will be presented today during a special late-breaking oral session at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, IL (abstract #LBA1008).
In a prespecified interim analysis, Enhertu plus pertuzumab reduced the risk of disease progression or death by 44% versus THP (based on a hazard ratio [HR] of 0.56; 95% confidence interval [CI] 0.44-0.71; p<0.00001). Median PFS was 40.7 months with Enhertu plus pertuzumab compared to 26.9 months for THP, as assessed by blinded independent central review (BICR). The PFS benefit for Enhertu plus pertuzumab versus THP was consistent across subgroups, including for the prespecified stratification factors of de novo or recurrent disease, hormone receptor status and PIK3CA mutation status.
Investigator-assessed PFS demonstrated a median PFS of 40.7 months for Enhertu plus pertuzumab compared to 20.7 months for THP (HR 0.49; 95% CI 0.39-0.61; nominal p-value <0.00001).
Confirmed objective response rate (ORR) with Enhertu plus pertuzumab was 85.1% versus 78.6% with THP. There were 58 complete responses (CRs) with Enhertu plus pertuzumab compared to 33 with THP. Median duration of response (DOR) for Enhertu plus pertuzumab exceeded three years (39.2 months) versus 26.4 months with THP.
Overall survival (OS) was not mature at the time of the interim analysis (16% maturity at data cut-off); however, interim OS data showed an early trend favouring the Enhertu combination compared to THP (HR 0.84; 95% CI 0.59-1.19).
Sara Tolaney, MD, MPH, Chief of the Division of Breast Oncology, Dana-Farber Cancer Institute and principal investigator in the trial, said: “Patients with HER2-positive metastatic breast cancer often experience disease progression around two years after initiating standard-of-care first-line treatment. With a median progression-free survival of more than three years, the DESTINY-Breast09 results show trastuzumab deruxtecan combined with pertuzumab has the potential to become a new first-line standard of care for these patients.”
Susan Galbraith, Executive Vice President, Oncology Haematology R&D, AstraZeneca, said: “Bringing Enhertu earlier in the treatment of HER2-positive metastatic breast cancer may represent an important advancement for patients. The DESTINY-Breast09 trial showed the combination of Enhertu and pertuzumab in the first-line setting substantially increased the amount of time before a patient’s cancer progressed compared to standard of care and nearly doubled the number of patients showing no signs of disease on imaging. Establishing a strong therapeutic response as soon as metastatic disease is diagnosed is critical given that about one in three patients do not receive further treatment after progressing in the first-line setting.”
Ken Takeshita, Global Head, R&D, Daiichi Sankyo, said: “Enhertu continues to transform the treatment of metastatic breast cancer with the first new data in more than a decade to demonstrate improved outcomes for a broad population of patients with HER2-positive disease compared to THP in the first-line setting. DESTINY-Breast09 shows that initiating treatment with Enhertu in combination with pertuzumab at the time of metastatic diagnosis can delay disease progression.”
Median duration of follow-up was nearly 2.5 years (29.2 months). As of the data cut-off, 302 (39.6%) patients remained on treatment, 174 in the Enhertu plus pertuzumab arm and 128 in the THP arm.
The safety profile of Enhertu in combination with pertuzumab in DESTINY-Breast09 was consistent with the known profiles of each individual therapy with no new safety concerns identified. Interstitial lung disease (ILD)/pneumonitis occurred in 12.1% of patients treated with Enhertu in combination with pertuzumab, as determined by an independent adjudication committee. The majority of ILD events were low Grade (Grade 1 [n=17; 4.5%] or Grade 2 [n=27; 7.1%]). There were no Grade 3 or Grade 4 ILD events. There were two Grade 5 (0.5%) ILD events in the Enhertu plus pertuzumab arm.
An additional investigational arm of the trial assessing Enhertu monotherapy versus THP remains blinded to patients and investigators and will continue to the final PFS analysis.
Enhertu is a specifically engineered HER2-directed DXd antibody drug conjugate (ADC) discovered by Daiichi Sankyo and being jointly developed and commercialised by Daiichi Sankyo and AstraZeneca.
Enhertu is already approved in more than 80 countries as 2nd-line treatment for patients with HER2-positive breast cancer based on the results from the DESTINY-Breast03 trial.
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