The IMPACT trial results: Tuesday April 27, 2009


OK … so here are the results we have all been waiting for for the past few weeks — the data from the IMPACT trial comparing the survival of patients treated with three doses of sipuleucel-T (Provenge) to placebo in men with androgen-independent prostate cancer.

As a reminder, the IMPACT trial only enrolled patients who met the following criteria:

  • Pathologically documented diagnosis of prostate cancer
  • Androgen-independent disease, as defined by disease progression while receiving “adequate” hormone therapy
  • Metastasis only to lymph nodes and bones (i.e., patients with soft tissue metastases to organs like the lung or liver were not eligible)
  • Absence of or minimal prostate cancer-related pain
  • A life expectancy of at least 6 months
  • A castrate level of testosterone (< 50 ng/dl)

The number of patients enrolled in the trial was 512, randomized 2:1 to receive sipuleucel-T or placebo. This meant that 341 patients were treated with sipuleucel-T and 171 with placebo.

Patients were followed with bone scans to show progression. On progression, patient were treated at the discretion of their physicians, but the patients who had been randomized to receive placebo were eligible to receive a frozen version of sipuleucel-T based on their cells at the time of original extraction.

The results of the study are as follows:

  • The average age of patients receiving sipuleucel-T was 72 years compared to 70 years for patients receiving placebo
  • The average PSA level of patients receiving sipuleucel-T was 51.7 ng/ml as compared to 47.2 ng/ml for patients receiving placebo.
  • Median overall survival for patients receiving sipuleucel-T was 25.8 months.
  • Median overall survival for patients receiving placebo was 21.7 months.
  • There was a 4.1 month increase in overall survival for patients treated with sipuleucel-T.
  • 31.7 percent of sipuleucel-T patients were alive at 3 years as compared to 23.0 percent of placebo patients.

Clearly, sipuleucel-T provided a statistically and clinically significant survival benefit compared to placebo. What is more, this survival benefit is twice as long as that offered by docetaxel in the studies that led to approval of that drug for a similar (but slightly more advanced) population of patients.

The most common side effects of sipuleucel-T reported in this trial were similar to those shown in prior studies of this treatment: chills in 54.1 percent of patients, pyrexia (fever) in 29.3 percent, and headache in 16 percent. Most of these side effects occurred within 2 days of each of the three rounds of drug infusion.

The “New” Prostate Cancer InfoLink notes that sipuleucel-T certainly appears to have met the criteria for approval set by the US Food and Drug Administration in 2007, so we should be able to look forward to its approval soon.

2 Responses

  1. What is the median time before progression for the treatment and placebo groups respectively?

  2. Good question. As far as I know this information is not available yet.

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