Juno Therapeutics said it has suspended a clinical trial of a cancer drug after two patients suffered swelling of the brain and died.

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Juno Therapeutics said Wednesday it has suspended a Phase II clinical trial of a cancer drug after two patients suffered swelling of the brain and died.

This is the second time the trial has been suspended in the past six months because of patient deaths.

The news sent Juno shares plunging as much as 32 percent in early trading Wednesday, the lowest point since the heavily funded Seattle biotechnology company went public in a hugely successful stock-market debut nearly two years ago. The stock closed the regular trading day Wednesday at $22.56, down 24.5 percent.

The company’s “Rocket” trial for B cell acute lymphoblastic leukemia — or ALL — is testing a drug it calls JCAR015. The trial involves using engineered T-cells designed to attack cancer cells to treat adult patients who have relapsed acute lymphoblastic leukemia.

The same trial had been temporarily suspended in July after two other patient deaths, but the company blamed those primarily on an additional drug added to the treatment. It subsequently changed that protocol.

The two earlier deaths also resulted from swelling in the brain, called cerebral edema. At the time, the company said it had added a chemotherapy drug called fludarabine to the trial. Juno was able to restart the Rocket trial after it removed fludarabine from the treatment.

Executives said Wednesday that they still believe removing fludarabine was the right move, though they reiterated that the deaths were likely caused by more than one factor.

“We did not expect the removal of fludarabine to eliminate entirely the risk of neurotoxicity or cerebral edema,” Chief Medical Officer Mark Gilbert said on a call with analysts Wednesday.

The four patients who died had symptoms that followed a similar timeline to each other, including developing a fever within the first few days after receiving the treatment.

A fifth patient died earlier this year from cerebral edema, which was the first death of a patient in the trial. Juno said it can’t confirm the death was related to treatment, and the trial was not placed on hold at that time.

Juno CEO Hans Bishop emphasized Wednesday that patients in the trial are facing extremely limited options for cancer treatment.

“We are faced with a difficult decision considering the encouraging early efficacy data in this trial and the poor prognosis of these relapsed, refractory ALL patients who have few, if any, treatment options,” he said on the conference call.

It is too early to say if the trial will be canceled, modified or continue with the same course, the company said. Juno executives are expected to give more information at the company’s investor conference Dec. 5.

Juno said Wednesday it notified the Food and Drug Administration of the voluntary hold and is working with the agency and the Data and Safety Monitoring Board to determine the next steps.

Juno’s trials and plans for its other product candidates are not affected, the company said. The company is testing a similar drug, JCAR017, for pediatric acute lymphoblastic leukemia patients. There have been no deaths in the trial, which has treated 43 patients.

Twenty-four patients with chronic lymphocytic leukemia have been treated with another drug, JCAR014, and one died as a result of the treatment. That drug was also used to treat 41 patients with Non-Hodgkin lymphoma, and two patients died. The company said it is no longer using the dose that was given to patients who died in that trial.

Gilbert said the company is optimistic about the benefits of the Rocket trial drug to treat cancer.

“I think it’s important to say, we see a likely path forward for JCAR015 and ALL but it’s just too early right now to speak to that with regards to the actual risk-benefits profile and that’s what we’re primarily going to judge this on,” he said.

Juno’s fast rise to success was heralded as a major win for the biotech industry in Washington state after its trials treating cancer showed early hopeful results.

The company went public in late 2014 as the biggest biotech IPO of the year. Its stock price rose 45 percent on its first day of trading.