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AstraZeneca, Daiichi Sankyo to Begin Regulatory Talks to Expand Enhertu Into HER2-Low Breast Cancer

NEW YORK – AstraZeneca and Daiichi Sankyo on Monday said that in the Phase III DESTINY-Breast04 trial advanced breast cancer patients with low HER2-expressing tumors had longer progression-free and overall survival on Enhertu (trastuzumab deruxtecan) compared to those on physicians' choice of chemotherapy.

The data, which the codevelopers of Enhertu have been anticipating, will likely support regulatory filings for the drug in the HER2-low metastatic breast cancer population. "We look forward to sharing the detailed findings of DESTINY-Breast04 with the medical community and initiating discussions with regulatory agencies globally with the goal of bringing Enhertu to patients with metastatic breast cancer previously considered to be HER2-negative," Ken Takeshita, Daiichi Sankyo's global head of R&D, said in a statement.

The DESTINY-Breast04 trial involves previously treated, advanced breast cancer patients who have hormone receptor (HR)-positive or -negative tumors. All patients had testing to determine HER2-low status, which was defined as an immunohistochemistry score of 1+ or 2+ and a negative in situ hybridization score.

Patients with this level of HER2 expression comprise 55 percent of breast cancer patients and are ineligible for currently marketed HER2-targeted treatments. Chemotherapy is the standard treatment right now for HR-positive breast cancer patients once they progress on hormone therapy and for HR-negative patients.

According to the sponsors, DESTINY-Breast04 met its primary endpoint and showed that previously treated HR-positive, HER2-low metastatic breast cancer patients on Enhertu had "superior" progression-free survival compared to those on standard chemo. The trial also met its secondary endpoint and showed that HER2-low patients regardless of HR status lived longer without their tumors progressing on Enhertu compared to those in the comparator arm. Overall survival was also significantly better for those on Enhertu.

The study didn't raise any new safety concerns with Enhertu treatment. Interstitial lung disease rates were similar to those observed in clinical trials involving later-line Enhertu treatment, the companies said.

Enhertu is already approved in the US and other countries as a treatment for advanced HER2-positive breast cancer patients following two or more anti-HER2 regimens. AstraZeneca and Daiichi Sankyo believe that the data from this latest trial could significantly expand the eligible population for its drug and change how breast cancer is classified and treated.

"A HER2-directed therapy has never before shown a benefit in patients with HER2-low metastatic breast cancer," Susan Galbraith, AstraZeneca's executive VP of oncology R&D, said in a statement. "These results for Enhertu are a huge step forward and could potentially expand our ability to target the full spectrum of HER2 expression, validating the need to change the way we categorize and treat breast cancer."