On 23 May, the clinical-stage biotechnology company Prothena Corporation, announced that its Phase III AFFIRM-AL clinical trial of birtamimab did not meet its primary endpoint of improving time to all-cause mortality. The study also failed to show benefit in either of its secondary measures: the 6-minute walk test distance and Short Form-36 version 2 Physical Component Score. Birtamimab was generally safe and well-tolerated, consistent with its established safety profile. Based on these results, the company will discontinue all development of birtamimab, including stopping the open label extension of the AFFIRM-AL clinical trial. The company is initiating a broad corporate restructuring. A substantial workforce reduction, estimated at approximately 63%, has recently been announced to substantially reduce the operating costs to those necessary to support the remaining wholly owned programs, the obligations to partnered programs and the anticipated business development activities.
The Phase 3 AFFIRM-AL clinical trial was a global, double-blind and placebo-controlled study that enrolled 207 newly diagnosed people with amyloid light-chain (AL) amyloidosis, which is the most common form of systemic amyloidosis. They received birtamimab or placebo by intravenous infusion monthly and also received concurrent standard of care therapy consisting of a first line regimen that contains a drug called bortezomib. Despite the setback, Prothena is looking forward to the initial data from Phase I ASCENT clinical trials of its PRX012 programme in Alzheimer’s disease expected in August and is following partnered programmes being developed for a number of other neurodegenerative diseases.
Press release announcing the results of the AFFIRM-AL clinical trial: https://ir.prothena.com/investors/press-releases/news-details/2025/Prothena-Announces-Phase-3-AFFIRM-AL-Clinical-Trial-for-Birtamimab-in-Patients-with-AL-Amyloidosis-Did-Not-Meet-Primary-Endpoint/default.aspx
Press release outlining Prothena’s corporate restructuring plan: https://ir.prothena.com/investors/press-releases/news-details/2025/Prothena-Announces-Corporate-Restructuring/default.aspx
