AstraZeneca and Daiichi Sankyo's Enhertu (trastuzumab deruxtecan) has been approved in the US for the treatment of adult patients with unresectable or metastatic HER2-positive breast cancer who have received a prior anti-HER2-based regimeneither in the metastatic setting, or in the neoadjuvant or adjuvant setting and have developed disease recurrence during or within six months of completing therapy. Enhertu is a specifically engineered HER2-directed antibody drug conjugate (ADC) being jointly developed and commercialised by AstraZeneca and Daiichi Sankyo. The approval by the Food and Drug Administration (FDA) was based on positive results from the DESTINY-Breast03 Phase III trial that showed Enhertu reduced the risk of disease progression or death by 72% versus trastuzumab emtansine (T-DM1) (hazard ratio [HR] 0.28; 95% confidence interval [CI]: 0.22-0.37; p<0.0001) in patients with HER2-positive unresectable and/or metastatic breast cancer previously treated with trastuzumab and a taxane.

The approval was granted under the FDA's Real-Time Oncology Review (RTOR) programme and converts the accelerated approval of Enhertu in later line HER2-positive metastatic breast cancer to standard approval, broadening Enhertu's breast cancer indication in the US to earlier lines of use in patients with HER2-positive metastatic breast cancer. The DESTINY-Breast03 Phase III trial results were recently published online in The New England Journal of Medicine.1 In the trial, the safety profile of Enhertu was consistent with previous clinical trials, with no new safety concerns identified and no Grade 4 or 5 treatment-related interstitial lung disease events. Based on the DESTINY-Breast03 data, fam-trastuzumab deruxtecan-nxki (Enhertu) recently was added to the NCCN Clinical Practical Guidelines in Oncology (NCCN Guidelines®) as the Category 1 preferred regimen as second-line therapy for recurrent unresectable (local or regional) or Stage IV HER2-positive disease.

The US regulatory submission was reviewed under Project Orbis, which provides a framework for concurrent submission and review of oncology medicines among participating international partners. Five national health authorities collaborated with the FDA on this review, including the Australian Therapeutic Goods Administration, the Brazilian Health Regulatory Agency (ANVISA), Health Canada, Israel's Ministry of Health Pharmaceutical Administration and Switzerland's Swissmedic. Regulatory applications for Enhertu are currently under review in Europe, Japan and several other countries for the treatment of adult patients with unresectable or metastatic HER2-positive breast cancer who have received a prior anti-HER2-based regimen based on the results from the DESTINY-Breast03 trial.

Following this approval for Enhertu in the US, an amount of $100m is due from AstraZeneca to Daiichi Sankyo as a 2nd-line milestone payment in HER2-positive metastatic breast cancer. In AstraZeneca, the milestones paid will be capitalised as an addition to the upfront payment made in 2019 and subsequent capitalised milestones and amortised through the profit and loss. Sales of Enhertu in the US are recognised by Daiichi Sankyo.

AstraZeneca reports its share of gross profit margin from Enhertu sales in the US as collaboration revenue in the Company's financial statements. For further details on the financial arrangements, please consult the collaboration agreement from March 2019. Breast cancer is the most common cancer and is one of the leading causes of cancer-related deaths worldwide and in the US.3,4 More than two million patients with breast cancer were diagnosed in 2020, with nearly 685,000 deaths globally.3More than 290,000 new cases are expected in the US in 2022, with more than 43,000 deaths.5Approximately one in five cases of breast cancer are considered HER2-positive.

HER2 is a tyrosine kinase receptor growth-promoting protein expressed on the surface of many types of tumours including breast, gastric, lung and colorectal cancers.7 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. Despite initial treatment with trastuzumab and a taxane, patients with HER2-positive metastatic breast cancer will often experience disease progression.9 More treatment options are needed to further delay progression and extend survival. DESTINY-Breast03 is a global, head-to-head, randomised, open-label, registrational Phase III trial evaluating the efficacy and safety of Enhertu (5.4mg/kg) versus T-DM1 in patients with HER2-positive unresectable and/or metastatic breast cancer previously treated with trastuzumab and a taxane.

The primary efficacy endpoint of DESTINY-Breast03 is progression-free survival (PFS) based on blinded independent central review. Secondary efficacy endpoints include overall survival, objective response rate (ORR), duration of response, PFS based on investigator assessment and safety.