Seattle Genetics' breast cancer drug hits mark in pivotal trial

Shares in Seattle Genetics, a company with a $14.8 billion market cap, rose 9% in premarket trading. (Seattle Genetics)

A pivotal trial of Seattle Genetics’ tucatinib in patients with HER2-positive breast cancer has met its primary endpoint. The data tee Seattle Genetics up to file for FDA approval of a TKI inhibitor it paid $614 million to acquire last year.

The trial tested tucatinib in combination with Roche’s Herceptin and Xeloda in patients with locally advanced unresectable or metastatic HER2-positive breast cancer. Subjects in the control cohort just received the two Roche drugs. All participants had previously taken Herceptin and two other Roche HER2 drugs: Perjeta and the antibody-drug conjugate Kadcyla.

Seattle Genetics linked the addition of tucatinib to the backbone combination to a 46% reduction in the risk of disease progression or death, resulting in the trial meeting its primary endpoint.

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The pivotal study also met two secondary endpoints. Investigators associated tucatinib with a 34% drop in the risk of death. That result was enough for the trial to hit a secondary endpoint that looked at overall survival. Tucatinib also outperformed Herceptin and Xeloda in a subset of patients who had brain metastases at baseline, chalking up a 52% reduction in the risk of disease progression or death. 

Those efficacy findings validate the confidence Seattle Genetics showed when it paid $614 million to buy Cascadian Therapeutics last year and suggest tucatinib can carve out a space in the breast cancer treatment pathway.

Currently, there are a lack of good options for patients who progress after treatment with Kadcyla. Tucatinib could address that gap. Equally, the significant minority of HER2-positive breast cancer patients who develop brain metastases need better treatments. The subanalysis shared by Seattle Genetics suggests tucatinib can help those patients, too.  

The only possible concerns revealed in the data shared today relate to the safety of tucatinib. While Seattle Genetics said the drug was generally well tolerated and showed a manageable safety profile, there were some differences in the rates of adverse events in the tucatinib and control arms. Almost 5% of patients on tucatinib had elevated levels of a liver damage biomarker, compared to less than 1% in the control group. 

Seattle Genetics is now gearing up to find out what regulators make of the data. A filing for FDA approval is planned for the first quarter of 2020. If successful, Seattle Genetics will get a shot at muscling in on a HER-positive breast cancer market dominated by Roche.

Shares in Seattle Genetics, a company with a $14.8 billion market cap, rose 9% in premarket trading. 

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