The action comes more than three years after an FDA advisory panel recommended approval, declaring the immune therapy safe and effective. But FDA concerns over efficacy led the FDA to delay a decision until more data became available.
Provenge doesn't cure prostate cancer or prevent it from getting worse over time. But it does extend survival -- by months for most patients, by years for some.
Provenge isn't your everyday vaccine. It's an immune therapy created by harvesting immune cells from a patient, genetically engineering them to fight prostate cancer, and then infusing them back into the patient.
It's approved only for treatment of asymptomatic or minimally symptomatic patients with prostate cancer that has spread outside the prostate and no longer responds to hormone therapy.
In clinical trials, Provenge extended survival by a median 4.1 months -- about half of patients were below that amount and half were above. But some of the patients remain alive years after the treatment. In the most recent trial, 32% of Provenge-treated patients remained alive three years after treatment. Only 23% of placebo-treated patients survived that long.
The approval makes Provenge the first cancer treatment vaccine. It will "re-energize" work in a field that is littered with disappointing failures, says Robert Dreicer, MD, chairman of Cleveland Clinic's department of solid tumor oncology. Dreicer helped run a Provenge clinical trial but has no financial interest in the product.
"If you asked me two years ago if I thought we were on the cusp of a cancer-treatment vaccine, I would have said no -- and I would have been wrong," Dreicer tells WebMD. "Now we are about to see a series of therapeutic vaccines that will not be curative, but which will allow us to manage many advanced cancers in a chronic disease paradigm."
The treatment won't be inexpensive. Industry analysts' estimate of Provenge's cost range from $40,000 to $100,000, with most analysts betting on the high end of the range. And the treatment presents a logistical challenge, as cells taken from patients must be transported to Dendreon facilities, treated with Provenge and tested for purity and potency, and then returned to a doctor for infusion.
Ongoing clinical trials are looking at whether Provenge might have more dramatic effects if given earlier in the course of prostate cancer. One of these studies is giving Provenge to men intending to undergo prostatectomy for prostate cancer that is still confined to the prostate gland. Investigators will examine the removed prostate tissue for signs that Provenge is reducing prostate tumors.
How Provenge Works
Once a cancer grows beyond a certain point, the immune system has a hard time fighting it. One reason is that cancer cells look a lot to the immune system like normal cells. Another reason is that tumors may give off signals that manipulate the immune system into leaving them alone.
Provenge bypasses these problems. The treatment first removes a quantity of dendritic cells from a patient's blood. Dendritic cells are antigen-presenting cells -- that is, they show pieces of an offending microbe or tumor to immune cells, priming them to attack cells that carry those pieces (antigens).
The patient's doctor ships the cells to Dendreon, which then exposes them to Provenge. Provenge is a molecule made inside genetically engineered insect cells. The molecule marries prostatic acid phosphatase (PAP) -- a marker found on nearly all prostate cancer cells -- to an immune-stimulating factor called GM-CSF.
Once these cells have been exposed to the Provenge molecule, they're shipped back to the doctor who infuses them back into the patient. This is done three times in one month. The first infusion primes the immune system. The second and third doses spur an anticancer immune response.
But so far, Provenge has been remarkably safe. However, clinical trials suggested the treatment might be linked to a slightly increased risk of stroke. Treated patients will be closely monitored to see if this risk is real.