Review showed 20 more deaths in treatment arm versus control arm of study.

Cell Genesys is halting a late-stage investigation of its prostate cancer immunotherapy because of an imbalance of deaths between the two treatment arms. A specific cause for this imbalance is yet unknown. No new safety issues were observed at the time of the review.

The firm’s stock took a major hit in morning trading. It dropped almost 74% from $2.8 per share at yesterday’s close to open today at $0.73.

“We are currently notifying all participating clinical trial sites and regulatory agencies that enrollment of new patients into Vital-2 has been suspended as has treatment with GVAX immunotherapy for prostate cancer of patients enrolled in the study,” says Stephen A. Sherwin, M.D., chairman and CEO.

The study, called Vital-2, was comparing GVAX in combination with Taxotere® to Taxotere plus prednisone in patients with advanced-stage prostate cancer. Cell Genesys reports that 408 patients had been enrolled to date.

In a routine safety review conducted earlier this week, the company’s Independent Data Monitoring Committee (IDMC) noted that 67 deaths occurred in the GVAX plus Taxotere treatment arm and 47 deaths occurred in the control arm.
Cell Genesys also plans on conducting an inspection of its second Phase III study with GVAX in prostate cancer, called Vital-1. The firm has requested that the IDMC perform a futility analysis of Vital-1, and results are expected in approximately one month.

Vital-1 is designed to compare GVAX as a monotherapy to Taxotere chemotherapy plus prednisone in earlier stage hormone-refractory patients with metastatic disease. It has enrolled 626 patients, and after a January interim analysis, IDMC recommended that the firm continue the trial.

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