BOTHELL, Wash. ( TheStreet) -- Seattle Genetics ( SGEN) announced Monday results from a pivotal study demonstrating that 75% of patients with advanced Hodgkin lymphoma responded for greater than six months to treatment with the experimental drug brentuximab vedotin.

The positive results from the study are strong enough to allow Seattle Genetics to seek U.S. regulatory approval for brentuximab in the first half of next year, the company said.

Seattle Genetics shares closed Friday at $12.16.

Brentuximab, also known as SGN-35, is designed using a technology proprietary to Seattle Genetics that delivers a lethal dose of chemotherapy directly to cancer cells while sparing healthy cells from toxic effects. Brentuximab consists of an antibody that attaches itself to a certain receptor found on tumor cells. Once inside the tumor, brentuximab releases a toxic chemotherapy payload.

The pivotal phase study was designed under a Special Protocol Assessment (SPA) with the U.S. Food and Drug Administration. Just over 100 patients with Hodgkin lymphoma were enrolled in the study, all of whom had disease that was no longer responsive to currently approved therapies, including autologous stem cell transplants.

After treatment with brentuximab, 75% of the patients demonstrated either a complete or partial response. The duration of response was greater than six months. The drug's safety profile was "consistent" with previous studies, Seattle Genetics said. Additional details from the study are being withheld so they can be presented at a future medical meeting.

"Few drugs ever demonstrate this level of response in the refractory setting, " said Seattle Genetics CEO Clay Siegall, in an interview Sunday. " We believe brentuximab provides a real opportunity and hope for Hodgkin patients in this setting for which there has been no major advance in years."

The FDA did not specify a brentuximab response rate necessary for the drug to be approved as a new treatment for Hodgkin lymphoma, but Seattle Genetics said previously that a 25-30% response rate lasting at least six months would be considered robust.

A previous, smaller study of brentuximab yielded response rates in the range of 50-60%.

About 8,500 patients in the U.S. each year are diagnosed with Hodgkin lymphoma, a cancer that affects white blood cells. Most of these patients are treated successfully with a four-drug chemotherapy cocktail or stem-cell transplants. Seattle Genetics intends to seek approval for brentuximab initially in the approximately 30% of patients who do not respond to current therapies or relapse.

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