Prothena Shares Drop 36.8% After Birtamimab Failure, Four Consecutive Earnings Misses
Prothena shares have plunged 36.8% over the past year following the termination of its wholly owned anti-amyloid candidate birtamimab after a failed AFFIRM-AL study. The company missed earnings estimates by an average of 26.7% over four quarters and now relies solely on collaboration revenues from partners including Bristol Myers Squibb.
1. Share Performance & Earnings Misses
Prothena shares have fallen 36.8% over the past year while the industry rose 19.6%. The company posted four consecutive quarters of earnings misses, averaging a 26.72% negative surprise driven by elevated research and development expenses and absence of near-term product revenues.
2. Birtamimab Termination Impact
In May 2025, Prothena halted its late-stage AFFIRM-AL trial of birtamimab after it failed to meet its primary endpoint. The termination removed its only wholly owned late-stage asset and eliminated the most immediate value driver for the stock.
3. Collaboration Revenue and Partnerships
With no commercial products, Prothena depends entirely on partnership milestones and royalties. It has received $100 million from Novo Nordisk for coramitug and $135 million from Roche for prasinezumab, with potential combined milestones exceeding $1.85 billion.
4. Future Pipeline and Development Timeline
Prothena is redirecting resources to early-stage assets such as PRX012 and PRX019, with a phase I trial for PRX019 expected to complete in 2026. Bristol Myers Squibb’s anti-tau antibody PRX005 is in phase II with primary completion slated for 2027.