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Seattle Genetics CEO Clay Siegall. (Seattle Genetics Photo)

Seattle Genetics, a Bothell, Wash., based biotechnology company developing novel treatments for cancer, announced Monday that it has discontinued the late-stage trial of its treatment for blood cancers after finding higher rates of death in patients taking the drug than the control group.

The company did not disclose how many patients had died in that trial.

Seattle Genetic’s stock price fell fourteen percent in premarket trading but rebounded, hovering at a four to five percent drop in the early morning. As of publishing, the company’s shares were trading at $61.99, about four percent below previous market close.

The company’s drug candidate — vadastuximab talirine — was being studied as a treatment for acute myeloid leukemia (AML) in older patients, a disease that currently has few effective treatments. It was the most advanced trial in the company’s current pipeline.

The drug was also being studied in an early stage trial of blood disorder myelodysplastic syndrome, which was also discontinued today.

Seattle Genetics said it would stop enrollment and treatment in the two trials while it evaluated next steps, meaning the trials could either be revived with new procedures or pulled entirely in the coming months.

Trials of the same drug were placed on hold by the FDA late last year after six patients developed serious liver damage, six of whom died. In a press release, Seattle Genetics said that the most recent deaths don’t appear to be related to liver failure, and noted a high rate of fatal infections among the patients who died in the trial.

“This is a disappointing and unexpected result for the CASCADE trial. Patient safety is our highest priority, and we will closely review the data and evaluate next steps,” said Seattle Genetics President and CEO Clay Siegall in a press release. “AML is a devastating disease with a poor prognosis in most patients, and there is a great need for therapeutics against this disease. We thank the patients, caregivers and investigators for their support of this trial.”

Seattle Genetics is developing antibody-drug conjugates to treat cancer. The treatments use a combination of antibodies, the immune cells that find and identify harmful agents like viruses and bacteria, and cancer-killing drugs to target treatment to cancer cells.

It has one of the first antibody-drug conjugate treatments on market: Adcetris, which is used to treat a variety of blood cancers.

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