Prothena slumps on Phase III birtamimab miss

Shared of Ireland-headquartered Prothena Corporation (Nasdaq: PRTA) plummeted almost 24% to $5.01 in post-market activity on Friday, when the company announced the Phase III AFFIRM-AL clinical trial evaluating birtamimab in patients with amyloid light chain (AL) amyloidosis did not meet its primary endpoint (HR=0.915, p-value=0.7680).

Based on these results, Prothena will discontinue the development of birtamimab, including stopping the open label extension of the AFFIRM-AL clinical trial, and prompting the company to implement cash preservation measures. The news has contributed to the stock’s significant decline from its 52-week high of $25.42.

“This is not the outcome that we expected, and we are surprised and disappointed by these results for patients, their families and caregivers, and for the entire AL amyloidosis community,” said Gene Kinney, president and chief executive of Prothena. “With these results, we believe that the most appropriate action is to discontinue all development of birtamimab,” he added.