Researchers affiliated with the IMPACT trial have reported that additional follow-up and more analyses demonstrate a clear survival advantage of Provenge® (sipuleucel-T) versus placebo in men with hormone-refractory prostate cancer. The details of this study were presented at the 2010 Genitourinary Cancers Symposium in San Francisco between March 5 and 7.[1]

Provenge is an active cellular immunotherapeutic agent that targets the prostatic acid phosphatase (PAP) antigen. The PAP antigen is present in approximately 95% of all prostate cancers. Published Phase I and II studies of Provenge in patients with prostate cancer show the approach using activated cellular immunotherapy with Provenge is safe and provides a potential benefit. Two previous trials (D9901 and D9902A) included a total of 225 patients. Patients were randomly allocated to receive Provenge or placebo; placebo patients received Provenge after disease progression. In the original analysis, patients randomized to Provenge had a 47% reduction in the risk of death compared with placebo. A subsequent analysis of these data suggested that Provenge improved the survival of patients with asymptomatic metastatic androgen-independent prostate cancer who received the vaccine followed by Taxotere® (docetaxel) at progression.

To evaluate the effect of Provenge among men with metastatic, androgen-independent prostate cancer, researchers conducted a Phase III clinical trial known as IMPACT (IMmunotherapy for Prostate AdenoCarcinoma Treatment). The trial enrolled 512 men. Study participants were treated with either Provenge (n-341) or a placebo (171). The median follow-up of this study is now 36.5 months.

• Median overall survival (OS) was 25.8 months for Provenge and 21.7 months for placebo.
• OS results were consistent in patients at low or high risk.
• The hazard ratio (HR) for survival was 0.76 for the Provenge group.
• The 36-month survival was 32% for the Provenge group versus 23% for the placebo group.

Comments: These data confirm the survival advantage of Provenge over placebo for men with hormone-refractory prostate cancer. It is anticipated that these findings will result in FDA approval of Provenge.

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