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June 19 (Reuters) - U.S. drug developer Seattle Genetics Inc said on Monday it would halt a late-stage study of its drug to treat a type of leukemia in old patients, after seeing a "higher rate" of deaths in patients taking the drug compared to those on a placebo.
The company did not disclose the number of deaths in the study.
Shares of Seattle Genetics fell 14 percent to $55.50 in premarket trading.
The drug, vadastuximab talirine, was being evaluated in the study to treat a form of blood cancer called acute myeloid leukemia (AML).
In December, the U.S. Food and Drug Administration (FDA) had imposed a clinical hold on several early-stage studies testing vadastuximab talirine after six AML patients were identified with liver toxicity and four died. The hold has since been lifted.
On Monday, Seattle Genetics said based on available data that the deaths in the late-stage AML study were not related to liver toxicity.
However, the company said it would suspend patient enrollment and treatment in all of its clinical trials involving vadastuximab talirine, including its early-stage trial of the drug in patients with another form of blood cancer.
Seattle Genetics said it would consult the FDA regarding future plans for the development of vadastuximab talirine. (Reporting by Akankshita Mukhopadhyay in Bengaluru; Editing by Sai Sachin Ravikumar)