Prothena's Late-Stage Study for AL Amyloidosis Fails, Stock Down

Core Viewpoint - Prothena (PRTA) shares fell 22.5% after the company announced the discontinuation of birtamimab development due to the failure of the AFFIRM-AL clinical study to meet its primary endpoint [1][5]. Group 1: Birtamimab Development - Birtamimab was a potential best-in-class anti-amyloid antibody aimed at treating AL amyloidosis, evaluated in a phase III global clinical trial with 207 newly diagnosed patients [3][4]. - The primary endpoint of time to all-cause mortality was not met, nor were the secondary endpoints, including the 6-minute walk test and Short Form-36 Physical Component Score [5]. - Despite the failure, birtamimab was reported to be generally safe and well-tolerated [5]. Group 2: Future Plans and Pipeline - Following the discontinuation of birtamimab, Prothena will reduce ongoing operating expenses and organizational size, with further updates expected in June [6]. - The company is also evaluating prasinezumab for Parkinson's disease in collaboration with Roche, which has reported mixed results from the phase IIb PADOVA study [7][8]. - Prothena is advancing early-stage programs for neurological indications, including BMS-986446 for Alzheimer's disease and PRX019 for neurodegenerative diseases, with ongoing clinical trials expected to complete in 2027 and 2026, respectively [9][10].