Seattle Genetics Inc said four people had died in trials testing its experimental cancer drug, prompting the U.S. Food and Drug Administration to impose a clinical hold on several early-stage studies.
The company's shares fell 14.6 percent to $52.85 in premarket trading.
Six patients with acute myeloid leukemia (AML), a type of blood cancer, have been identified with liver toxicity and four have died, the company said on Tuesday.
The company is working with the FDA to identify whether the drug is the cause of the toxicity.
The clinical holds have been initiated to evaluate the potential risk of liver toxicity in patients who were treated with the drug and underwent a stem cell transplant either before or after treatment.
The drug, vadastuximab talirine, has been evaluated in more than 300 patients, and will continue to be tested in ongoing late-stage study in older AML patients, the company said.
The drug is also being tested in patients with myelodysplastic syndrome, another form of blood cancer.
(Reporting by Divya Grover in Bengaluru; Editing by Shounak Dasgupta and Maju Samuel)