Shares of Aastrom Biosciences Inc. plunged 35.6 percent Thursday after the company reported interim analysis data from its Phase IIb study in critical limb ischemia showing that its autologous cell therapy hit the primary endpoint, but failed to show statistical significance in a key secondary endpoint of amputation-free survival.

The stock (NASDAQ:ASTM) lost $1.49 to close at $2.71.

Aastrom stated in its press release that the RESTORE-CLI study was not powered to demonstrate statistical significance in that secondary endpoint. Data showed a reduction in the event rates of 24 percent (p = 05541).

Nevertheless, Wall Street had been hoping for better. The company's stock had run up more than 100 percent in the two weeks ahead of Thursday's presentation at the satellite session of the VEITHsymposium in New York, where investors had anticipated seeing the similar data as disclosed in the first interim analysis back in June. Those earlier data, which demonstrated a 50 percent to 60 percent increase in amputation-free survival, were so strong, Aastrom's drug safety monitoring board recommended halting the trial early and moving right into Phase III.

The Ann Arbor, Mich.-based firm filed a special protocol assessment for a pivotal CLI study last month. (See BioWorld Today, Oct. 21, 2010.)

Results from the second interim analysis of all 86 patients showed that the Phase IIb study met both its primary and secondary endpoint of time to first occurrence of treatment failure (p = 0.0132). Further analysis showed a clinically meaningful reduction of 56 percent in treatment failure events.