FDA eyes trial size for Seattle Genetics cancer drug

Seattle Genetics’ experimental cancer drug showed promise in treating two rare types of blood cancer, but the design and size of clinical trials limited conclusions, U.S. drug reviewers said.

Food and Drug Administration staff also said the trials for the drug, under the proposed trade name Adcetris, had “significant” missing safety data, in documents released on Tuesday.

The FDA is reviewing Adcetris for use in previously treated patients with Hodgkin’s lymphoma and anaplastic large cell lymphoma (ALCL), both types of blood cancer. About 9,000 Americans are diagnosed with Hodgkin’s lymphoma a year, and 3,000 with ALCL.

Shares of the U.S. biotechnology company Seattle Genetics fell 2.6 percent to $20 in morning Nasdaq trading. They hit an all-time high of $21.41 on June 28 after European health regulators accepted an application to market the drug for those uses.

In preliminary trials, Adcetris, which is given in a 30-minute infusion every three weeks, demonstrated complete response rates and reduced tumor size in more than 90 percent of patients—94 percent for Hodgkin’s and 97 percent for ALCL, the company said.

However, the second-stage trials only included 58 patients for ALCL and 102 patients for Hodgkin’s, and did not compare the Adcetris to another drug. The FDA said these factors “limit the benefit-risk analysis.”

The FDA reviewers also noted that no second trial confirms the clinical benefit of Adcetris in patients with ALCL, as required under priority review, and asked the advisory panel to weigh whether the drug should be granted an accelerated approval without such a confirmatory trial.

CLOSE TO $1 BILLION SALES

The company’s Chief Executive Clay Siegall told Reuters in May that U.S. annual sales of Adcetris for Hodgkin’s and ALCL would likely amount to less than $1 billion.

But if the drug wins approval as a front-line therapy, or first treatment option, annual U.S. sales could be “considerably over a billion dollars,” Siegall said, adding that he had a “high level of confidence” that Adcetris will win U.S. approval by August 30—the early decision date set by the FDA.

Cory Kasimov, a JPMorgan analyst, sees an 85 percent chance the drug will receive approval for both indications.

“That said, we still believe that expansion in earlier stages of disease with larger patient markets is critical to the stock’s future valuation,” he added in a note.

The FDA granted priority review status for the drug, known chemically as brentuximab vedotin, meaning the agency believes the medicine to be a potentially significant therapeutic advance over existing therapies.

Brentuximab vedotin links a tumor-targeting antibody to a cancer-killing chemotherapy drug with the goal of limiting side effects. It is designed to home in on an antigen, or foreign substance, expressed in Hodgkin’s lymphoma, several types of T-cell lymphoma and other hematologic malignancies.

Seattle holds full U.S. and Canadian rights to Adcetris, while Japanese drugmaker Takeda Pharmaceutical Co has rights for the rest of the world, with milestone payments and royalties going to Seattle.

On June 27, Seattle said it would receive a $5 million milestone payment under that collaboration agreement after the European Medicines Agency accepted an application to market the drug for Hodgkin’s and ALCL in Europe.

Seattle has said it was also testing the drug in other types of lymphoma.

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By Alina Selyukh and Anna Yukhananov

WASHINGTON