Thursday's rally in Dendreon shares is the latest in a string of dramatic share-price flip-flops for the Seattle-based drugmaker, whose stock tumbled just three weeks ago after the FDA said it would need more data before it could approve Provenge. On other occasions, the stock has staged major rallies, when prospects for Provenge appeared on the upswing.
Dendreon on May 9 said the FDA had issued an "approvable letter" for the product but wanted additional data supporting its effectiveness, suggesting a likely delay for the vaccine that jolted investors and the stock.
The company subsequently cut 40 jobs connected with marketing of the product, or about 18 percent of its work force.
Jonathan Aschoff, an analyst with Brean Murray & Co., said Dendreon shares jumped Thursday because the FDA had signaled the ongoing study would answer remaining questions, and thatanother big trial will not be needed.
"Some people thought another trial might have to be conducted, but this one -- if it succeeds -- will be sufficient," Aschoff said.
But Aschoff said Thursday's rally for Dendreon shares was unwarranted because the ongoing study will likely fail its primary goals, as did two earlier Phase 3 trials.
"If this one fails, it will be the third time around" and likely doom the medicine, he said.
The FDA in January accepted Dendreon's marketing application for Provenge on a "fast-track" basis, based in part on suggestions it might be able to prolong survival.
An FDA advisory panel in March said Provenge appeared reasonably safe and there was "substantial evidence" of its benefits, causing shares to triple.
The stock's roller-coaster movements have been due to uncertainty created by mixed trial data. Although a pair of Dendreon studies failed to meet their main goal of slowing progress of advanced prostate cancer, one analysis found patients treated with Provenge survived about 4.5 months longer than those receiving placebos.
Aschoff said that prolonged-survival data was seen in a trial whose design may have favored Provenge, by including too many sicker patients in the placebo group and not enough suchpatients in the group taking the vaccine.
Provenge has been studied in men with prostate cancer who had stopped responding to hormone therapy but were not having pain.
If approved, the product could boost prospects for other therapeutic vaccines, including ones being developed by GlaxoSmithKline for a range of cancers.