The Food and Drug Administration has approved a first-of-a-kind prostate cancer treatment that uses the body's immune system to fight the disease, offering an important alternative to decades-old approaches.

Dendreon Corp.'s Provenge vaccine trains the immune system to fight tumors. It's called a "vaccine" even though it treats disease rather than prevents it.

Doctors have been trying to develop such a therapy for decades, and Provenge is the first to successfully prolong patient lives.

The drug is intended to treat cancer that has spread elsewhere in the body and is not responding to hormone therapy. Provenge is made by taking immune cells from a patient's blood and exposing them to a protein found in most prostate cancers. That encourages the cells to attack the cancer.

Provenge is given intravenously, with a total of three doses given approximately once every two weeks. The agency said 192,000 new cases of prostate cancer were diagnosed in 2009, and 27,000 men died of the disease. Prostate cancer most often affects older men.

Side effects of Provenge include chills, fatigue, fever, back pain, nausea, joint ache, and headache, the FDA said.

Shares of Seattle-based Dendreon jumped 19 percent to new highs ahead of the news, rising to an all-time high of $47.32. Trading of the stock was halted at 12:34 p.m. Eastern, 35 minutes before the FDA announced its decision. At the time, Dendreon shares were up $5.88, or 14.8 percent, at $45.50.

The company does not have any products on the market. Prostate cancer is usually treated with surgery, radiation, or medicine that blocks testosterone.

The only drug approved to treat advanced prostate cancer is Sanofi-Aventis's Taxotere, a chemotherapy agent. Last year, Dendreon said a clinical trial showed patients treated with Provenge lived for about a month longer than men treated with Taxotere.

Sanofi-Aventis is also working on a new drug for advanced prostate cancer called Jevtana. That drug is related to Taxotere, but may be better at improving survival.