Roche and Prothena are advancing prasinezumab, a Parkinson's disease antibody, into Phase 3 trials despite previous mid-stage studies missing primary endpoints. Analysts at Jefferies estimate only a 25% to 40% probability of success for the late-stage study, citing concerns over the antibody’s ability to target alpha-synuclein effectively. Roche emphasizes encouraging signals in early-stage patients and biomarker data but acknowledges the need to refine patient selection. The new trial's design details remain undisclosed, and Prothena recently announced layoffs following another clinical setback.