Prothena Corp. Plc (PRTA)

Prothena's stock price has experienced fluctuations in the past six months. From April 4, 2025, to April 2, 2026, the share price declined, but in the past month and six months, it saw increases. Longer-term, the stock decreased over two and three years. In March 2026, Prothena announced a clinical milestone payment from Novo Nordisk related to the ongoing Phase 3 clinical trial for Coramitug. In February 2026, the company announced a share repurchase plan and reported its Fourth Quarter and Full Year 2025 financial results. In November 2025, Prothena reported its Third Quarter 2025 financial results, highlighting partnered Phase 3 starts, program milestones, and capital plans. In June 2025, the Phase 3 AFFIRM-AL clinical trial for birtamimab did not meet its primary endpoint, leading to the discontinuation of the program and a workforce reduction, which likely negatively impacted the stock.

As a clinical-stage biotechnology company, Prothena Corporation Plc does not have approved products generating sales revenue, so traditional demand seasonality does not apply. Its revenue is primarily derived from collaboration milestones from its partners, which are tied to clinical or regulatory achievements rather than seasonal consumer demand.

Prothena Corporation Plc is a late-stage clinical biotechnology company focused on discovering and developing novel therapies for diseases caused by protein dysregulation, operating within the Healthcare sector and Biotechnology industry. The company develops therapies for neurodegenerative and rare peripheral amyloid diseases, leveraging its expertise in protein dysregulation. Its pipeline includes partnered and wholly-owned programs such as Prasinezumab, an investigational humanized monoclonal antibody in Phase 3 clinical trials for Parkinson's disease and other synucleinopathies, developed in partnership with Roche. Coramitug is a potential first-in-class amyloid depleter antibody for the treatment of ATTR amyloidosis with cardiomyopathy, which is in Phase 3 clinical trials and partnered with Novo Nordisk. BMS-986446 is an anti-MTBR-tau-targeting antibody in Phase 2 for early Alzheimer's disease, developed in collaboration with Bristol Myers Squibb. PRX019 is a program targeting undisclosed neurodegenerative diseases, partnered with Bristol Myers Squibb. TDP-43 CYTOPE and PRX012-TfR are programs targeting Amyotrophic lateral sclerosis (ALS) and Alzheimer's disease, respectively. Birtamimab was previously in development for AL amyloidosis, but its Phase 3 trial did not meet its primary endpoint, leading to its termination and a workforce reduction in June 2025. PRX123 is a dual Aβ/tau vaccine for Alzheimer's disease.

Prothena Corporation Plc is headquartered in Dublin, Ireland, with significant operations in the United States and a presence in several other countries worldwide.

Prothena's brand reputation has been shaped by its progress in clinical development and strategic corporate actions. The termination of the birtamimab program and subsequent workforce reduction likely had a negative impact, while positive developments in partnered late-stage programs and the achievement of a clinical milestone payment from Novo Nordisk contributed positively. Leadership team updates indicate ongoing corporate development and strategic planning.

Prothena Corporation Plc has a significant institutional ownership base, with 193 institutional owners holding a total of 46,105,798 shares as of April 10, 2026, including Fmr Llc, BlackRock, Inc., and Rubric Capital Management LP. Major individual/insider owners include Ecor1 Capital LLC and Oleg Nodelman. Elan Corp PLC also holds a significant stake.