Juno Therapeutics Plunges 30% After 2 Patient Deaths From Lead Cancer Drug

Juno Therapeutics Inc JUNO was halted shortly after Thursday's closing bell. A couple minutes later, the company announced JCAR015's Phase 2 trial was put on hold after two patients died last week.

"JCAR015 therapy is being tested among adult patients with acute lymphoblastic leukemia [and] was placed on hold by the FDA," said Juno CEO Hans Bishop, according to Forbes' Luke Timmerman. "More than 20 patients had enrolled in the Rocket study thus far. While the hold is in effect, no new patients will be enrolled, and no additional doses will be given to existing patients."

At 4:35 p.m. ET, the stock reopened for trading down about 30 percent at $28.76.

"Juno believes that the deaths may have been related to the type of preconditioning therapy that patients got before having their re-engineered T-cell infusions," Timmerman continued. "The patients who died in the Rocket trial got fludarabine and cyclophosphamide as preconditioning drugs to deplete certain blood cells, and create what scientists think is a more favorable environment for re-infused T-cells to engraft and start attacking cancer. Earlier Juno studies used only cyclophosphamide, which wasn’t associated with such severe neurotoxcity. Juno added fludarabine to the preconditioning regimen for the Rocket study during the second quarter.

The news also sent the SPDR S&P Biotech (ETF) XBI down about 1.3 percent in the after-hours session.

"It is a big deal," Otis Brawley, chief medical officer of the American Cancer Society, told Forbes' Matthew Herper. "But he's says he’s seen clinical holds resolved in the past, including with important drugs like Taxol. He says the fact that the deaths seem so clearly linked with fludarabine is a good sign."