Prothena (PRTA) 10K Form and Latest SEC Filings 2026

Prothena's fiscal year ends on December 31. The company typically files its 10-K annual report by the end of February, covering the prior fiscal year's financial results. Key financial data from these reports is available on Prothena's financial statements page.

The most recent filing was a Form 4 submitted on September 3, 2026. This was an insider ownership change filed by 4 - PROTHENA CORP PUBLIC LTD CO (0001559053) (Issuer).

SEC filings are legally required disclosures that public companies submit to the U.S. Securities and Exchange Commission. Unlike press releases or earnings call transcripts, these documents are filed under legal obligation — meaning the financial data they contain is audited, standardized, and subject to penalties if materially false. For investors, that makes SEC filings the most reliable primary source available for evaluating a company's true financial position.

Yes. All SEC filings are publicly available through the SEC's EDGAR database and on financial research platforms like MarketBeat. Companies are required by law to make these disclosures accessible to all investors — meaning retail investors have access to the same source documents as institutional analysts.

A 10-K is an annual report containing audited financial statements and a full review of the company's business — it is the most comprehensive filing a company makes each year. A 10-Q is a shorter, unaudited quarterly update filed three times per year between annual reports. Investors typically use the 10-K for deep fundamental analysis and the 10-Q to track whether the company is on pace with its guidance mid-year.

The most important filing for fundamental investors. Filed once per year, the 10-K contains audited financial statements, revenue and earnings trends, debt obligations, risk factors, and management's own assessment of the business. Reading the risk factors section and comparing year-over-year financials can reveal issues that don't show up in analyst summaries.

An unaudited financial update filed three times per year (the 10-K covers Q4). Investors use 10-Qs to track whether guidance is on pace, monitor changes in cash flow or inventory, and catch any mid-year shifts in business conditions before they become headline news.

Filed within four business days of a material event — earnings releases, merger announcements, executive departures, or major asset sales. Because 8-Ks are filed before media coverage catches up, they are often the fastest way to get unfiltered information directly from the company on market-moving events.

Filed within two business days whenever an executive or director buys or sells company stock. Insider purchases — especially large or clustered buys — are often interpreted as a signal of management confidence. Insider selling is more ambiguous but worth monitoring for patterns, particularly around lock-up expirations or ahead of major announcements.