AstraZeneca (AZN) and Daiichi Sankyo won breakthrough therapy designation from the US Food and Drug Administration for Enhertu, in combination with pertuzumab, as a treatment for adults with unresectable or metastatic HER2 positive breast cancer.

The designation was based on a Phase 3 trial of 1,157 patients across five continents that evaluated Enhertu, alone or with pertuzumab, against the standard first-line regimen of taxane, trastuzumab, and pertuzumab, the companies said Thursday in a statement.

Enhertu was discovered by Daiichi Sankyo and is being developed and commercialized jointly by the Tokyo-based company and AstraZeneca.

Shares of AstraZeneca fell 1.2% in recent Thursday trading.

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