Seagen stands by newly acquired HER2 breast cancer drug despite competition from AstraZeneca-Daiichi's Enhertu

AstraZeneca and Daiichi Sankyo's Enhertu posted eye-popping data in a recent breast cancer trial, showing its superiority to Roche's Kadcyla. But Seagen believes its newly acquired HER2 drug has the potential to compete. (Daiichi Sankyo/AstraZeneca)

After Seattle biotech Seagen paid for the rights to a HER2 breast cancer treatment in August, it got bad news a month later in the form of stellar results from a competing med.

Did Seagen make a bad buy when it paid Chinese company RemeGen $200 million upfront, with $2.4 billion in potential biobucks also on the line?

Thursday, when Seagen presented its third-quarter earnings, it stood by the potential of its new drug, disitamab vedotin (RC48).

Talking about the competitor product, Enhertu, Seagen CEO Clay Siegall said in a conference call that the “molecule internalizes, but it’s kind of a middle of the road internalization. The antibody used in RC48, which is what we licensed from RemeGen, was selected based on incredibly rapid internalization.”

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There’s a lot to like about disitamab vedotin. It’s already been approved for stomach cancer in China, making it the first antibody-drug conjugate (ADC) developed in the country to be endorsed anywhere. In the U.S., it has breakthrough-therapy designation for second-line HER2-positive bladder cancer.

At the European Society for Medical Oncology conference last month, when AstraZeneca and Daiichi Sankyo presented data on Enhertu, it was evident that the companies had a potential game changer in breast cancer.

In the Enhertu trial, the drug made waves by cutting the risk of disease progression or death by 72% over rival Kadcyla, from Roche, in second-line HER2-positive metastatic breast cancer patients who were previously treated with Roche’s Herceptin and chemo.  

But both Enhertu and Kadcyla are cut from the same cloth, as they use Herceptin as their antibody. Meanwhile, the antibody component for Seagen’s new drug, disitamab, is a novel medicine.

Compared to Enhertu and Kadcyla, disitamab vedotin has superior tumor-binding ability and tumor uptake, Seagen says. That’s what was attractive to Seagen, which has established itself as perhaps the premier developer of ADCs thanks largely to its payload-linker technology.

Seagen already has a HER2 small-molecule treatment in Tukysa, which was approved for breast cancer in April of last year. In the third quarter, Tukysa rolled up $87 million in sales, more than double its first full quarter on the market ($42 million) last year.

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“I think we're in a fortunate position in that we have a highly valuable and active small molecule Tukysa. We now have a HER2-directed antibody with properties that we think are very interesting,” Seagen’s chief medical officer Roger Dansey said. “And we have the external environment, which includes drugs like Kadcyla, which we're exploring in combination with Tukysa. So there are lots of possibilities for us going forward.”

Sales of Seagen’s lymphoma treatment Adcetris, which has been on the market for a decade, came in at $185 million, a 13% increase from last year’s third quarter. Padcev, which was approved for bladder cancer in 2019, came in at $95 million, an increase of 54% on last year’s performance.