Osiris' Prochymal fails two Phase III studies in GvHD; shares plunge

Preliminary data showed that Osiris' experimental stem-cell therapy Prochymal failed to meet the primary endpoints of two late-stage trials in patients with acute graft-versus-host disease (GvHD), the company reported Tuesday. Osiris' shares dropped as much as 40 percent on the news.

The placebo-controlled studies enrolled a combined total of 452 patients. In the first trial, which had a primary endpoint of complete resolution of GvHD for at least 28 days, patients with steroid-refractory acute GvHD administered Prochymal plus standard of care achieved a response rate of 35 percent, compared to 30 percent for those who received standard of care alone, data indicated.

The second trial involved patients with newly diagnosed acute GvHD. It assessed the proportion of patients who achieved a complete response who survived at least 90 days after receiving Prochymal plus steroid therapy, versus patients who took steroids alone. The findings showed that the Prochymal group achieved a 45-percent response rate, compare to 46 percent for those who took only steroids.

Osiris CEO C. Randal Mills noted that further analysis of the data is required, and added that the company will meet with the FDA "as soon as possible to discuss the most appropriate and efficient path forward for Prochymal" in the GvHD indication. The treatment is also undergoing late-stage testing in patients with Crohn's disease.

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