Results, Setbacks

Slammed by more deaths, Seattle Genetics scraps a PhIII study and pulls back (again) on vadastuximab

Clay Siegall

Just three months after the FDA lifted a clinical hold on its late-stage cancer drug vadastuximab talirine (SGN-CD33A), the biotech abruptly scrapped a Phase III study and halted enrollment across a slate of studies after independent monitors tracked a higher rate of deaths among patients taking its drug.

The deaths in the study — for frontline use against acute myeloid leukemia — included fatal infections but were evidently not associated with liver toxicity, which had already killed 4 patients, forcing the FDA to hit the brakes on the study in late December, 2016.

The latest safety crisis will hit Seattle Genetics $SGEN hard. The company had been reporting positive data on the drug, its most advanced experimental drug in the pipeline, and analysts were looking for new ways for the company to expand beyond Adcetris. Just a few weeks ago Seattle Genetics was also forced to throw the towel in on a $2 billion deal to collaborate with Immunomedics, further limiting its late-stage effort.

The company’s stock dropped 12% on the news, marking the loss of about $1 billion in market cap.

Data at one point for vadastuximab demonstrated that 15 of 23 (65%) evaluable patients achieved CR/CRi. At a median follow-up of 7.7 months, median survival had not yet been reached, and 72 percent of patients remained alive and on study.

Back in March the biotech reported that it was getting restarted on the clinical work after it came up with “revised eligibility criteria and stopping rules for veno-occlusive disease.” The FDA agreed to lift the hold only two months after it was dropped on Seattle Genetics. And the agency may face questions about why it was so quick to agree to the green light, given the recent deaths.

Seattle Genetics CEO Clay Siegall tried to shift the focus to the positive. He noted:

“We are enthusiastic about the many opportunities across our broad pipeline, including ADCETRIS (brentuximab vedotin), enfortumab vedotin (ASG-22ME) and SGN-LIV1A. Notably, we are looking forward to reporting data from our ADCETRIS phase 3 ECHELON-1 trial in frontline Hodgkin lymphoma, and we are on track to advance enfortumab vedotin into a pivotal trial in metastatic urothelial cancer in the second half of 2017 under our collaboration with Astellas.”

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