CHICAGO—Sipuleucel-T (Provenge), an experimental immunotherapeutic vaccine, prolonged survival in men with metastatic, androgen-independent prostate cancer, according to study findings presented here at the American Urological Association annual meeting.

The findings are based on data from the IMPACT (IMunotherapy for Prostate AdenoCarcinoma Treatment) study, a randomized, double-blind, placebo-controlled trial involving 512 patients. Patients treated with sipuleucel-T survived a median of 4.1 months longer than placebo recipients (25.8 vs. 21.7 months).

The vaccine, which is administered as an IV infusion, improved three-year survival by 38% (31.7% vs. 23%) and reduced the risk of death by 22.5% compared with placebo. The vaccine did not significantly delay time to progression. Adverse events observed more commonly in vaccine-treated patients were chills, fever, and headache. These evens were mainly low grade and lasted one to two days following infusion.

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The vaccine uses a patient’s own immune system to recognize and attack existing cancer cells. The vaccine is made by drawing blood from a patient, isolating the relevant immune cells, and then stimulating those cells to recognize, as foreign, prostatic acid phosphatase, a protein found on prostate cancer cells.