FDA OKs Provenge for Prostate Cancer Therapy
'Vaccine' Is an Immune Therapy That Treats Advanced Prostate Cancer
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.
The treatment is not without side effects. Nearly all patients suffer some mild to moderate adverse reactions such as chills, fatigue, fever, back pain, nausea, joint ache, and headache.
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.