Enhertu ® Approved in the EU as Adjuvant Treatment for Patients with Residual Disease After Neoadjuvant Treatment for HER2 Positive Early Breast Cancer

Enhertu^® (trastuzumab deruxtecan) has been approved in the European Union (EU) as a monotherapy for the adjuvant treatment of adult patients with resected HER2 positive (immunohistochemistry [IHC] 3+ or in-situ hybridization [ISH]+) breast cancer who have residual invasive disease after neoadjuvant taxane-based and HER2 targeted treatment.

Enhertu is a specifically engineered HER2 directed DXd antibody drug conjugate (ADC) discovered by Daiichi Sankyo (TSE: 4568) and being jointly developed and commercialized by Daiichi Sankyo and AstraZeneca (LSE/STO/NYSE: AZN).

The approval by the European Commission follows the positive opinionof the Committee for Medicinal Products for Human Use of the European Medicines Agency and is based on results from the DESTINY-Breast05 phase 3 trial presented at the 2025 European Society for Medical Oncology (#ESMO25) Congress and subsequently published in The New England Journal of Medicine.

In DESTINY-Breast05, Enhertu significantly reduced the risk of invasive disease recurrence or death (invasive disease-free survival [IDFS]) by 53% (hazard ratio [HR]=0.47; 95% confidence interval [CI]: 0.34-0.66; p<0.0001) compared to trastuzumab emtansine (T-DM1) in patients with HER2 positive breast cancer with residual invasive disease following neoadjuvant therapy. Enhertu demonstrated a three-year IDFS rate of 92.4% (95% CI: 89.7-94.4) and 83.7% with T-DM1 (95% CI: 80.2-86.7). Data also showed that Enhertu significantly reduced the risk of disease recurrence or death (disease-free survival [DFS]) by 53% (HR=0.47; 95% CI: 0.34-0.66; p<0.0001) compared to T-DM1. Results showed a three-year DFS rate of 92.3% (95% CI: 89.5-94.3) in the Enhertu arm and 83.5% with T-DM1 (95% CI: 79.9-86.4).

“For patients with HER2 positive early breast cancer and residual invasive disease after neoadjuvant therapy, reducing the risk of disease recurrence is critical for sustained long-term outcomes,” said Sibylle Loibl, MD, PhD, GBG (German Breast Group) and Goethe University Medicine Frankfurt, Frankfurt am Main and lead investigator of the DESTINY-Breast05 trial. “The EU approval of trastuzumab deruxtecan, which demonstrated a more than 50% reduction in risk of recurrence compared to standard of care in DESTINY-Breast05, has the potential to change how we treat eligible patients in this setting.”

In DESTINY-Breast05, the safety profile of Enhertu was consistent with the known profile with no new safety concerns identified. Grade 3 or grade 4 adverse reactions from a pooled safety analysis of 4,146 patients who received at least one dose of Enhertu (5.4 mg/kg) in clinical studies across multiple tumor types included neutropenia (18.7%), anemia (8.2%), fatigue (7.4%), leukopenia (6.6%), thrombocytopenia (5.4%), lymphopenia (5.0%), nausea (4.5%), increased transaminases (3.3%), hypokalemia (3.1%), pancytopenia (2.8%), diarrhea (2.1%), vomiting (2.0%), decreased appetite (1.4%) and pneumonia (1.2%). Grade 5 adverse reactions occurred in 0.9% of patients, including interstitial lung disease (ILD)/pneumonitis (0.8%).

“By bringing Enhertu into the adjuvant setting, we are advancing this treatment option earlier in the course of disease for patients with HER2 positive early breast cancer,” said Ken Keller, Global Head of Oncology Business, and President and CEO, Daiichi Sankyo, Inc. “This first approval of Enhertu in early breast cancer in the EU reflects our continued commitment to bringing innovative medicines into earlier treatment settings, where there is significant potential to improve long-term outcomes for patients.”

“The goal of treatment in early breast cancer is to help as many patients as possible achieve cure. Unfortunately, despite treatment advances, some patients still face recurrence in the long-term,” said Dave Fredrickson, Executive Vice President, Oncology Hematology Business Unit, AstraZeneca. “The approval of Enhertu in the adjuvant setting for patients with residual disease after neoadjuvant treatment has the potential to establish a new benchmark in this curative-intent setting, with more than 92% of patients alive and free of invasive disease at three years.”

Enhertu (5.4 mg/kg) is now approved in more than 35 countries/regions worldwide for the adjuvant treatment of adult patients with HER2 positive breast cancer who have residual invasive disease following neoadjuvant trastuzumab (with or without pertuzumab) and taxane-based treatment based on the DESTINY-Breast05 trial.

Financial Considerations
Following this approval in the EU, an amount of $75 million is due from AstraZeneca to Daiichi Sankyo as a milestone payment for the adjuvant HER2 positive early 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.

About DESTINY-Breast05
DESTINY-Breast05 is a global, multicenter, randomized, open-label, phase 3 trial evaluating the efficacy and safety of Enhertu (5.4 mg/kg) versus T-DM1 in patients with HER2 positive early breast cancer with residual invasive disease in breast or axillary lymph nodes following neoadjuvant therapy and a high risk of recurrence. High risk of recurrence was defined as presentation with inoperable cancer (prior to neoadjuvant therapy) or pathologically positive axillary lymph nodes following neoadjuvant therapy.

The primary endpoint of DESTINY-Breast05 is investigator-assessed IDFS, which is defined as the time from randomization until first invasive local, axillary or distant recurrence or death from any cause. The key secondary endpoint is investigator-assessed DFS. Other secondary endpoints include overall survival, distant recurrence-free interval, brain metastases-free interval and safety.

DESTINY-Breast05 enrolled 1,635 patients in Asia, Europe, North America, Oceania and South America. For more information about the trial, visit ClinicalTrials.gov.

About HER2 Positive Early Breast Cancer
Breast cancer is the most common cancer in women worldwide and the leading cause of cancer-related deaths among women.¹ Approximately 2.4 million breast cancer cases were diagnosed in 2024, with more than 690,000 deaths globally.¹ In Europe, approximately 540,000 cases of breast cancer were diagnosed in 2024, with more than 140,000 deaths.²

HER2 is a tyrosine kinase receptor growth-promoting protein expressed on the surface of many types of tumors including breast cancer.³ HER2 protein overexpression may occur as a result of HER2 gene amplification and is often associated with aggressive disease and poor prognosis in breast cancer.³ Approximately one in five cases of breast cancer is considered HER2 positive.⁴

Approximately one in three patients with HER2 positive early-stage breast cancer is considered high-risk, meaning they are more likely to experience disease recurrence and have a poor prognosis.⁵ Despite receiving additional treatment with current standard of care for residual disease, some patients still experience invasive disease or death.⁶ Once patients are diagnosed with metastatic disease, the five-year survival rate drops from nearly 100% to approximately 34%.⁷

Adjuvant therapy represents a key opportunity to minimize the risk of recurrence and prevent progression to metastatic disease for patients with residual disease.^8,9,10 Prior to the approval of Enhertu in the HER2 positive adjuvant (after surgery) setting for patients with residual invasive disease, the standard of care was T-DM1.¹¹

About Enhertu
Enhertu (trastuzumab deruxtecan; fam-trastuzumab deruxtecan-nxki in the U.S. only) is a HER2 directed ADC. Designed using the proprietary DXd ADC Technology of Daiichi Sankyo, Enhertu is the lead ADC in the oncology portfolio of Daiichi Sankyo and the most advanced program in AstraZeneca’s ADC scientific platform. Enhertu consists of a HER2 monoclonal antibody attached to a number of topoisomerase I inhibitor payloads (an exatecan derivative, DXd) via tetrapeptide-based cleavable linkers.

Enhertu (5.4 mg/kg) followed by THP is approved in more than five countries/regions worldwide as a neoadjuvant treatment for adult patients with HER2 positive (IHC 3+ or ISH+) stage 2 or stage 3 breast cancer based on the results from the DESTINY-Breast11 trial.

Enhertu (5.4 mg/kg) is approved in more than 35 countries/regions worldwide for the adjuvant treatment of adult patients with HER2 positive breast cancer who have residual invasive disease following neoadjuvant trastuzumab (with or without pertuzumab) and taxane-based treatment based on the DESTINY-Breast05 trial.

Enhertu (5.4 mg/kg) in combination with pertuzumab is approved in more than 40 countries/regions worldwide as a first-line treatment for adult patients with unresectable or metastatic HER2 positive (IHC 3+ or ISH+) breast cancer, as determined by a locally or regionally approved test, based on the results from the DESTINY-Breast09 trial.

Enhertu (5.4 mg/kg) is approved in more than 100 countries/regions worldwide for the treatment of adult patients with unresectable or metastatic HER2 positive (IHC 3+ or ISH+) breast cancer who have received a prior anti-HER2-based regimen, either in the metastatic setting or in the neoadjuvant or adjuvant setting, and have developed disease recurrence during or within six months of completing therapy based on the results from the DESTINY-Breast03 trial.

Enhertu (5.4 mg/kg) is approved in more than 75 countries/regions worldwide 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, as determined by a locally or regionally approved test, that have progressed on one or more endocrine therapies in the metastatic setting based on the results from the DESTINY-Breast06 trial.

Enhertu (5.4 mg/kg) is approved in more than 100 countries/regions worldwide for the treatment of adult patients with unresectable or metastatic HER2 low (IHC 1+ or IHC 2+/ISH-) 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.

Enhertu (5.4 mg/kg) is approved in more than 80 countries/regions worldwide for the treatment of adult patients with unresectable or metastatic NSCLC whose tumors have activating HER2 (ERBB2) mutations, as detected by a locally or regionally approved test, and who have received a prior systemic therapy based on the results from the DESTINY-Lung02 and/or DESTINY-Lung05 trials. Continued approval in China and the U.S. for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial.

Enhertu (6.4 mg/kg) is approved in more than 90 countries/regions worldwide for the treatment of adult patients with locally advanced or metastatic HER2 positive (IHC 3+ or IHC 2+/ISH+) gastric or gastroesophageal junction (GEJ) adenocarcinoma who have received a prior trastuzumab-based regimen based on the results from the DESTINY-Gastric01, DESTINY-Gastric02 and/or DESTINY-Gastric04trials.

Enhertu (5.4 mg/kg) is approved in more than 50 countries/regions worldwide for the treatment of adult patients with unresectable or metastatic HER2 positive (IHC 3+) solid tumors who have received prior treatment and have no satisfactory alternative treatment options based on efficacy results from the DESTINY-PanTumor02, DESTINY-Lung01, DESTINY-CRC02, DESTINY-PanTumor03 and/or HERALD trials. Continued approval in China and the U.S. for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial.

About the Enhertu Clinical Development Program
A comprehensive global clinical development program is underway evaluating the efficacy and safety of Enhertu as a monotherapy or in combination or sequentially with other cancer medicines across multiple HER2 targetable cancers.

About the Daiichi Sankyo and AstraZeneca Collaboration
Daiichi Sankyo and AstraZeneca entered into a global collaboration to jointly develop and commercialize Enhertu in March 2019 and Datroway^® in July 2020, except in Japan where Daiichi Sankyo maintains exclusive rights for each ADC. Daiichi Sankyo is responsible for the manufacturing and supply of Enhertu and Datroway.

About the ADC Portfolio of Daiichi Sankyo
The Daiichi Sankyo ADC portfolio consists of nine ADCs in clinical development crafted from ADC technology discovered in-house by Daiichi Sankyo.

The DXd ADC Technology platform of Daiichi Sankyo consists of seven ADCs in clinical development where each ADC is comprised of a monoclonal antibody attached to a number of topoisomerase I inhibitor payloads (an exatecan derivative, DXd) via tetrapeptide-based cleavable linkers. The DXd ADCs include Enhertu and Datroway, which are being jointly developed and commercialized globally with AstraZeneca, and ifinatamab deruxtecan (I-DXd), raludotatug deruxtecan (R-DXd) and patritumab deruxtecan (HER3-DXd), which are being jointly developed and commercialized globally with Merck & Co., Inc., Rahway, NJ, USA. DS-3939 and DS3790 are being developed by Daiichi Sankyo.

Additional ADCs being developed by Daiichi Sankyo include DS3610, which consists of an antibody attached to a novel payload that acts as an agonist of STING, and DS1025, which consists of a CD25 directed antibody attached to an immuno-oncology optimized cytotoxic payload.

Ifinatamab deruxtecan, raludotatug deruxtecan, patritumab deruxtecan, DS-3939, DS3610, DS3790 and DS1025 are investigational medicines that have not been approved for any indication in any country. Safety and efficacy have not been established.

About Daiichi Sankyo
Daiichi Sankyo (TSE: 4568) is a global healthcare company committed to becoming a trusted healthcare innovator, transforming the lives of people through its strength in science and technology. The company discovers and develops new standards of care to address diverse medical needs to fulfill its purpose of contributing to the enrichment of quality of life around the world. With a strategic focus on oncology, Daiichi Sankyo is advancing an industry-leading antibody drug conjugate portfolio along with identifying new breakthrough generating technologies to deliver practice-changing medicines to patients, healthcare professionals and society. For more information, please visitwww.daiichisankyo.com.

REFERENCES
¹ World Health Organization. Global Status Report On Cancer 2026: The Future We Choose Together.Accessed October 2026.
² World Health Organization. Breast Fact Sheet. Accessed October 2026.
³ Cheng X. Genes. 2024;15(7):903.
⁴ Tarantino P, et al. Ann Oncol.2023;34(8):645-659.
⁵ Mahtani R, et al. Cancers (Basel). 2025;17(11):1848.
⁶ Geyer CE, et al. N Engl J Med. 2025;392(3):249-257.
⁷ National Cancer Institute. SEER Cancer Stat Facts: Female Breast Cancer Subtypes. Accessed October 2026.
⁸ von Minckwitz G, et al. N Engl J Med. 2019;380(7):617-628.
⁹ Zaborowski AM and Wong SM. BJS. 2023;110(7):765-772.
¹⁰ Loibl S, et al. N Engl J Med. 2026;394(9):845-857.
¹¹ Loibl S, et al. ESMO Clinical Practice Guidelines. 2024.

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