Despite falling short in mid-stage trials, Roche and Prothena are advancing prasinezumab, a Parkinson’s disease monoclonal antibody, into Phase III testing. Analysts remain cautious, assigning a 25% to 40% probability of success, questioning the antibody’s capacity to effectively target intracellular alpha-synuclein. The upcoming Phase III study aims to refine patient selection and evaluate clinical benefits suggested by “efficacy signals” and biomarker trends from Phase IIb trials. Prothena’s recent layoffs follow prior setbacks, but Roche highlights ongoing efforts to optimize study design and patient populations.