Juno Therapeutics is halting the study of an experimental leukemia treatment for a second time after the death of two more patients.
Two patients were reported dead in the closely-watched drug trial in July.
The Seattle company said Wednesday that the deaths occurred earlier this week after patients suffered a severe form of brain swelling, similar to the previous two. Company executives in July blamed the deaths on chemotherapy drugs used in a pre-treatment regimen, rather than on the company's experimental drug.
The Food and Drug Administration granted researchers permission to resume the study several days later.
Juno says it's working with regulators to determine what to do next.
Juno Therapeutics Inc. lost a quarter of its value in frenzied trading early Wednesday.