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Potential New Standard of Care in Previously Treated Breast Cancer Patients

September 20, 2021 • 3:39 pm CDT
(Vax Before Cancer)

The results of a phase 3 clinical study were presented today in a Presidential Symposium at the European Society for Medical Oncology Congress 2021.

Detailed positive results from the head-to-head DESTINY-Breast03 Phase III trial showed that Enhertu (trastuzumab deruxtecan), the AstraZeneca and Daiichi Sankyo Company, Limited (hereafter, Daiichi Sankyo) HER2-directed antibody-drug conjugate (ADC), demonstrated superior progression-free survival (PFS) versus trastuzumab emtansine (T-DM1), a HER2-directed ADC currently approved to treat patients with HER2-positive unresectable and/or metastatic breast cancer previously treated with trastuzumab and a taxane.

At a prespecified interim analysis of DESTINY-Breast03, Enhertu demonstrated a 72% reduction in the risk of disease progression or death compared to T-DM1 (hazard ratio [HR] 0.28; 95% confidence interval [CI] 0.22-0.37; p=7.8x10-22).

After 15.5 and 13.9 months of follow-up in the Enhertu and T-DM1 arms, respectively, the median PFS for patients treated with Enhertu was not reached (95% CI 18.5-NE) compared to 6.8 months for T-DM1 (95% CI 5.6-8.2) as assessed by blinded independent central review (BICR).

In the key secondary endpoint of PFS assessed by investigators, patients treated with Enhertu experienced a three-fold improvement in PFS of 25.1 months versus 7.2 months for T-DM1 (HR 0.26; 95% CI 0.20-0.35; p=6.5x10-24).

A consistent PFS benefit was observed in key subgroups of patients treated with Enhertu, including those with a history of stable brain metastases.

There was a strong trend towards improved overall survival (OS) with Enhertu (HR 0.56; 95% CI 0.36-0.86; nominal p=0.007172).

However, this analysis is not yet mature and is not statistically significant.

Nearly all patients treated with Enhertu were alive at one year (94.1%) compared to 85.9% of patients treated with T-DM1.

The confirmed objective response rate (ORR) doubled in the Enhertu arm versus the T-DM1 arm (79.7% vs. 34.2%). Forty-two (16.1%) complete responses (CR) and 166 (63.6%) partial responses (PR) were observed in patients treated with Enhertu compared to 23 (8.7%) CRs and 67 (25.5%) PRs in patients treated with T-DM1.

Javier Cortés, M.D., Ph.D., Head, International Breast Cancer Center, Barcelona, stated in a press release, “Patients with previously treated HER2-positive metastatic breast cancer will typically experience disease progression in less than a year with available HER2-directed treatments."

"The high and consistent benefit was seen across efficacy endpoints, and key subgroups of patients receiving Enhertu in DESTINY-Breast03 is remarkable and supports the potential of Enhertu to become the new standard of care for those who have previously been treated for HER2-positive metastatic breast cancer.”

Breast cancer remains the most common cancer and is one of the leading causes of cancer-related deaths in women worldwide.1 More than two million patients with breast cancer were diagnosed in 2020, resulting in nearly 685,000 deaths globally.

Approximately 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 tumors, including breast, gastric, lung, and colorectal cancers.3 HER2 protein overexpression may occur due to HER2 gene amplification and is often associated with aggressive disease and a poor prognosis in breast cancer.

Daiichi Sankyo and AstraZeneca entered into a global collaboration to jointly develop and commercialize Enhertu (a HER2-directed ADC) in March 2019 and datopotamab deruxtecan (DS-1062; a TROP2-directed ADC) in July 2020, except in Japan where Daiichi Sankyo maintains exclusive rights. Daiichi Sankyo is responsible for the manufacturing and supply of Enhertu and datopotamab deruxtecan.

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