Enhertu granted Breakthrough Therapy Designation in the US for patients with HER2-low metastatic breast cancer

Based on DESTINY-Breast04 results where AstraZeneca and Daiichi Sankyo’s Enhertu demonstrated a significant improvement in both progression-free survival and overall survival

Enhertu has now been granted five Breakthrough Therapy Designations, including three in breast cancer and one in both lung and gastric cancers

The Food and Drug Administration’s (FDA) BTD is designed to accelerate the development and regulatory review of potential new medicines that are intended to treat a serious condition and address a significant unmet medical need. The new medicine needs to have shown encouraging preliminary clinical results that demonstrate substantial improvement on a clinically significant endpoint over available medicines.

Up to half of all patients with breast cancer have tumours with a HER2 immunohistochemistry (IHC) score of 1+, or 2+ in combination with a negative in-situ hybridisation (ISH) test, a level of HER2 expression not currently eligible for HER2-targeted therapy.1-4 Low HER2 expression occurs in both HR-positive and HR-negative disease.5

HER2 testing is routinely used to determine appropriate treatment options for patients with metastatic breast cancer. Targeting the lower range of expression in the HER2 spectrum may offer another approach to delay disease progression and extend survival in patients with metastatic breast cancer.6 Currently chemotherapy remains the only treatment option for patients with HR-positive tumours following progression on endocrine (hormone) therapy.7 Few targeted options are available for those who are HR-negative.8

The FDA granted the BTD based on data from the pivotal DESTINY-Breast04 Phase III trial which reported positive high-level results in February 2022. In the trial, Enhertu demonstrated a statistically significant and clinically meaningful improvement in both progression-free survival (PFS) and overall survival (OS) in patients with HER2-low unresectable and/or metastatic breast cancer in all randomised patients with HR-positive and HR-negative disease versus physician’s choice of chemotherapy, which is the current standard of care. The safety profile of Enhertu was consistent with previous clinical trials with no new safety concerns identified. The data will be presented at an upcoming medical meeting.

Breast cancer and HER2 expression
Breast cancer is the most common cancer and is one of the leading causes of cancer-related deaths worldwide and in the US.9,10 More than two million cases of breast cancer were diagnosed in 2020 resulting in nearly 685,000 deaths globally.In the US, more than 290,000 new cases are expected to be diagnosed in 2022, resulting in more than 43,000 deaths.11

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, and is one of many biomarkers expressed in breast cancer tumours.12 HER2 expression is currently defined as either positive or negative, and is determined by an IHC test which measures the amount of HER2 protein on a cancer cell, and/or an ISH test which counts the copies of the HER2 gene in cancer cells.12,13 HER2-positive cancers are defined as IHC 3+ or IHC 2+/ISH+, and HER2-negative cancers are currently defined as IHC 0, IHC 1+ or IHC 2+/ISH-.12

DESTINY-Breast04
DESTINY-Breast04 is a global, randomised, open-label, registrational Phase III trial evaluating the efficacy and safety of Enhertu (5.4mg/kg) versus physician’s choice of chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel or nab-paclitaxel) in patients with HR-positive (n=480) or HR-negative (n=60) HER2-low unresectable and/or metastatic breast cancer previously treated with one or two prior lines of chemotherapy. Patients were randomised 2:1 to receive either Enhertu or chemotherapy.

The primary endpoint of DESTINY-Breast04 is PFS in patients with HR-positive disease based on blinded independent central review (BICR). Key secondary endpoints include PFS based on BICR in all randomised patients (HR-positive and HR-negative disease), OS in patients with HR-positive disease and OS in all randomised patients (HR-positive and HR-negative disease). Other secondary endpoints include PFS based on BICR and investigator assessment, duration of response based on BICR and safety.

DESTINY-Breast04 enrolled approximately 540 patients at multiple sites in Asia, Europe and North America. For more information about the trial, visit ClinicalTrials.gov.

Enhertu
Enhertu is a HER2-directed ADC. Designed using Daiichi Sankyo’s proprietary DXd ADC technology, Enhertu is the lead ADC in the oncology portfolio of Daiichi Sankyo and the most advanced programme in AstraZeneca’s ADC scientific platform. Enhertu consists of a HER2 monoclonal antibody attached to a topoisomerase I inhibitor payload, an exatecan derivative, via a stable tetrapeptide-based cleavable linker.

Enhertu (5.4mg/kg) is approved in more than 40 countries for the treatment of adult patients with unresectable or metastatic HER2-positive breast cancer who have received two or more prior anti-HER2-based regimens based on the results from the DESTINY-Breast01 trial.

Enhertu (6.4mg/kg) is approved in several countries for the treatment of adult patients with locally advanced or metastatic HER2-positive gastric or gastroesophageal junction (GEJ) adenocarcinoma who have received a prior trastuzumab-based regimen based on the results from the DESTINY-Gastric01 trial.

Enhertu development programme
A comprehensive development programme is underway globally, evaluating the efficacy and safety of Enhertu monotherapy across multiple HER2-targetable cancers, including breast, gastric, lung and colorectal cancers. Trials in combination with other anticancer treatments, such as immunotherapy, are also underway.

Regulatory applications for Enhertu are currently under review in Europe, Japan, the US 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.

Enhertu is also currently under review in the US for the treatment of adult patients with unresectable or metastatic non-small cell lung cancer (NSCLC) whose tumours have a HER2 (ERBB2) mutation and who have received a prior systemic therapy, and in Europe for the treatment of adult patients with locally advanced or metastatic HER2-positive gastric or GEJ adenocarcinoma who have received a prior anti-HER2 based regimen based on the DESTINY-Gastric01 and DESTINY-Gastric02 trials.

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