Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today announced that it will report its third quarter and first nine months of 2025 financial results on Thursday November 6, 2025, after the close of the U.S. financial markets.

Consistent with past practice, the Company will not be conducting a conference call in conjunction with the financial results release on November 6.

About Prothena

Prothena Corporation plc is a late-stage clinical biotechnology company with expertise in protein dysregulation and a pipeline of investigational therapeutics with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases. Fueled by its deep scientific expertise built over decades of research, Prothena is advancing a pipeline of therapeutic candidates for a number of indications and novel targets for which its ability to integrate scientific insights around neurological dysfunction and the biology of misfolded proteins can be leveraged. Prothena's pipeline includes both wholly-owned and partnered programs being developed for the potential treatment of diseases including ATTR amyloidosis with cardiomyopathy, Alzheimer's disease, Parkinson's disease and a number of other neurodegenerative diseases. For more information, please visit the Company's website at www.prothena.com and follow the Company on X (formerly Twitter) @ProthenaCorp.

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Mark Johnson, CFA, Vice President, Investor Relations

650-837-8550

IR@prothena.com

Media@prothena.com

Prothena to Report Third Quarter 2025 Financial Results on November 6