The FDA, despite a positive recommendation from its independent advisory panel, on May 8th indefinitely delayed approval of biologic drug Provenge, an experimental drug that works by mobilizing the body’s natural immune system to fight prostate cancer.
The FDA asked for additional clinical data on Provenge before approving it, Dendreon said in a press release. While Dendreon has had little to say about what information the FDA is seeking, the request seems likely to delay approval of Provenge for at least one and possibly as many as three years.
The company is a new clinical trial of Provenge, but full results aren’t expected for another two or three years.
“Given our strong belief in the survival benefit and safety profile of Provenge, coupled with the positive outcome of the Advisory Committee meeting, we are disappointed that this decision will cause a delay in the availability of Provenge for patients who suffer from advanced prostate cancer,” Mitch Gold, Dendreon’s CEO, said in a statement.
The Cellular, Tissue and Gene Therapies Advisory Committee on March 29th unanimously concluded that Provenge is safe, then concluded on a 13 to 4 vote that there is substantial evidence Provenge works against advanced prostate cancer that no longer responds to hormone treatment.
If the FDA had approved Provenge, it would have been the first therapeutic cancer vaccine to win regulatory approval. Unlike prophylactic vaccines approved to prevent diseases such as hepatitis B or cervical cancer, therapeutic vaccines are meant to treat an existing disease.
A number of other therapeutic cancer vaccines are in late-stage clinical trials.
Provenge uses special white blood cells called dendritic cells, which doctors harvest from a patient’s blood and send to a lab at Dendreon Corp. The cells are then mixed with a booster and an antigen that is abundant on the surface of nearly all prostate cancer cells but not on normal cells.
The resulting vaccine is then injected back into the patient. The dendritic cells present the prostate antigen to the body’s T cells, showing them which molecular targets to attack, and the T cells search out and destroy diseased cells carrying the antigen.
Neither of two small studies Dendreon submitted to the FDA achieved their primary goal of showing Provenge halted the advance of the cancer. The main study suggested the vaccine could extend the lives of patients by 4.5 months and a second smaller study showed a survival advantage of 3.3 months.
But panel members nevertheless concluded that there was “substantial evidence” that Provenge works.
