Daiichi Sankyo (TSE: 4568) and AstraZeneca’s (LSE/STO/Nasdaq: AZN) ENHERTU^® (trastuzumab deruxtecan) has been approved in the European Union (EU) as a monotherapy for the treatment of adult patients with unresectable or metastatic hormone receptor (HR) positive, HER2 low (IHC 1+ or IHC 2+/ISH-) or HER2 ultralow (IHC 0 with membrane staining) breast cancer who have received at least one endocrine therapy in the metastatic setting and who are not considered suitable for endocrine therapy as the next line of treatment.

ENHERTU is a specifically engineered HER2 directed DXd antibody drug conjugate (ADC) discovered by Daiichi Sankyo and being jointly developed and commercialized by Daiichi Sankyo and AstraZeneca.

The approval by the European Commission follows the positive opinion of the Committee for Medicinal Products for Human Use of the European Medicines Agency and is based on results from the DESTINY-Breast06 phase 3 trial presented at the 2024 American Society of Clinical Oncology (#ASCO24) Annual Meeting and published in The New England Journal of Medicine.

HR positive, HER2 negative is the most common breast cancer subtype, accounting for approximately 70% of all breast cancers.¹ Despite being classified as HER2 negative, many of these tumors still have some level of HER2 expression. Currently, regardless of HER2 expression, endocrine-based therapies are widely used in the early lines of treatment for HR positive metastatic breast cancer. Following endocrine-based therapy, some patients discontinue treatment, and others are treated with conventional chemotherapy which is associated with poor response rates and outcomes.^2,3,4,5

“This approval introduces a new treatment option for HR positive metastatic breast cancers that express HER2,” said Giuseppe Curigliano, MD, PhD, Professor of Medical Oncology at the University of Milan and the Head of the Division of Early Drug Development at the European Institute of Oncology, IRCCS, Italy and Principal Investigator of DESTINY-Breast06. “In DESTINY-Breast06, ENHERTU outperformed chemotherapy, providing progression-free survival of more than one year for patients with HR positive, HER2 low or HER2 ultralow metastatic breast cancer, demonstrating the benefit of treating these patients with ENHERTU instead of chemotherapy.”

In the DESTINY-Breast06 trial, ENHERTU demonstrated a 38% reduction in the risk of disease progression or death versus chemotherapy in patients with chemotherapy-naïve HR positive, HER2 low metastatic breast cancer (n=713; hazard ratio [HR] 0.62; 95% confidence interval [CI]: 0.52-0.75; p<0.0001) as assessed by blinded independent review (BICR). Median progression-free survival (PFS) was 13.2 months (95% CI: 11.4-15.2) in the ENHERTU arm compared to 8.1 months (95% CI: 7.0-9.0) in the chemotherapy arm.

The confirmed objective response rate (ORR) in the HER2 low population was 56.5% (95% CI: 51.2-61.7) in the ENHERTU arm versus 32.2% (95% CI: 27.4-37.3) in the chemotherapy arm. Median duration of response (DOR) was 14.1 months (95% CI: 11.8-15.9) in the ENHERTU arm versus 8.6 months (95% CI: 6.7-11.3) in the chemotherapy arm.

In the overall trial population of patients with chemotherapy-naïve HR positive, HER2 low or HER2 ultralow metastatic breast cancer (n=866), ENHERTU achieved a similar 36% reduction in the risk of disease progression or death versus chemotherapy (HR 0.64; 95% CI: 0.54-0.76; p<0.0001). A median PFS of 13.2 months (95% CI: 12.0-15.2) was seen in patients treated with ENHERTU compared to 8.1 months (95% CI: 7.0-9.0) in patients treated with chemotherapy.

Confirmed ORR in the overall trial population was 57.3% (95% CI: 52.5-62.0) in the ENHERTU arm versus 31.2% (95% CI: 26.8-35.8) in the chemotherapy arm. Median DOR was 14.3 months (95% CI: 12.5-15.9) in the ENHERTU arm versus 8.6 months (95% CI: 6.9-11.5) in the chemotherapy arm.

An exploratory analysis of the HER2 ultralow population (n=152; HR 0.78; 95% CI: 0.50-1.21) showed the clinically meaningful improvement in PFS was consistent between patients with HER2 low and HER2 ultralow expression, with 13.2 months (95% CI: 9.8-17.3) in patients treated with ENHERTU compared to 8.3 months (95% CI: 5.8-15.2) in those treated with chemotherapy. Confirmed ORR was 61.8% (95% CI: 50.0-72.8) in the ENHERTU arm versus 26.3% (95% CI: 16.9-37.7) in the chemotherapy arm. Median DOR was 14.3 months (95% CI: 9.2-20.7) in the ENHERTU arm versus 14.1 months (95% CI: 5.9, not estimable) in the chemotherapy arm.

“ENHERTU continues to evolve what is possible with breast cancer treatment, becoming the first HER2 directed medicine approved in the EU for patients with HR positive metastatic breast cancer with HER2 low or HER2 ultralow expression following endocrine therapy,” said Ken Keller, Global Head of Oncology Business, and President and CEO, Daiichi Sankyo, Inc. “Today’s approval expands the use of ENHERTU to now include an earlier treatment setting of HER2 low metastatic breast cancer and broadens the patient population eligible for treatment to those with HER2 ultralow disease.”

“ENHERTU continues to open up new approaches to the diagnosis and treatment of patients with metastatic breast cancer,” said Dave Fredrickson, Executive Vice President, Oncology Hematology Business Unit, AstraZeneca. “This approval underscores the importance of testing metastatic breast cancer tumors for any IHC staining to identify patients with HR positive, HER2 low or HER2 ultralow disease who may be eligible for ENHERTU once sustained responses are no longer achieved with endocrine-based therapy.”

In DESTINY-Breast06, the safety profile of ENHERTU was consistent with previous clinical trials with no new safety concerns identified. Grade 3 or grade 4 treatment-related adverse events from a pooled safety analysis of patients treated with ENHERTU (5.4 mg/kg) across multiple tumor types in clinical studies included neutropenia (18.0%), anemia (10.5%), fatigue (7.8%), leukopenia (6.0%), thrombocytopenia (5.4%), nausea (4.9%), lymphopenia (3.9%), hypokalemia (3.8%), transaminases increased (3.5%), diarrhea (2.5%), vomiting (2.4%), decreased appetite (1.8%), pneumonia (1.3%), and ejection fraction decreased (1.0%). Grade 5 adverse reactions occurred in 1.4% of patients, including interstitial lung disease (1.1%).

ENHERTU is already approved in more than 75 countries, including the EU, for patients with HER2 low metastatic breast cancer who have received a prior systemic therapy in the metastatic setting or developed disease recurrence during or within six months of completing adjuvant chemotherapy based on the results from the DESTINY-Breast04 trial.

Financial Considerations
Following this approval in the EU, an amount of $125 million is due from AstraZeneca to Daiichi Sankyo as a milestone payment for the HER2 low and HER2 ultralow chemotherapy-naive breast cancer indication. Sales of ENHERTU in most EU territories are recognized by Daiichi Sankyo. For further details on the financial arrangements, please consult the collaboration agreement from March 2019.