Researchers found that Dendreon’s immunotherapy drug Provenge prolonged the lives of advanced prostate cancer patients by an average of 4.1 months compared to a placebo. This figure represents a 20 percent increase in life for the patient. Dendreon presented the results of their 512-patient Phase 3 IMPACT study on Tuesday at the American Urological Association Annual Meeting. Among other discoveries, researchers found that Provenge increased the three-year survival rate by 38 percent, and reduced the risk of death by 28.5 percent. Provenge is designed for advanced prostate cancer patients who do not respond to hormone therapy. It is the first personalized cancer drug, using the patient’s own white cells to fight the disease. Patients are infused with an antigen created by the prostate cancer tumor. The antigen stimulates the patient’s immune system, creating white cells to battle the cancer. Each batch of Provenge works only for that patient. The most common side effect is a day or two of flu-like symptoms. The results are a big step forward for the Seattle company, which has had a difficult road to FDA approval. The FDA gave Provenge a favorable recommendation in 2007, but told the company they needed more data before approving the drug. The company plans to file an amended application with the FDA in the fourth quarter. Some analysts are now suggesting that the promising research results make Dendreon an attractive takeover target. The AUA presentation capped off a turbulent day on Wall Street for Dendreon. Half an hour before Tuesday's announcement, company shares mysteriously plunged almost 50 percent in 30 seconds of trading, reaching a low of $11.81. Nasdaq temporarily halted trading of Dendreon stock while they investigated the “potentially erroneous” trades, which they decided to let stand. Upon Dendreon’s announcement, company shares nearly doubled in after-hours trading. Analysts are still uncertain as to what caused Tuesday's plunge. Related link: Dendreon press release Related video: Dr. David Penson, M.D., University of Southern California, discusses the results of Dendreon's Provenge study.