Prothena Corporation plc (PRTA) Stock Price & Analysis

Prothena Corporation plc (PRTA) closed at USD 8.88 on Thursday, October 29, 2026, down 2.42% on the day. The US market is currently closed (after-hours); this is not a live price.

The prior close was USD 9.1; the Oct 29, 2026 session ranged USD 8.76–9.26 on volume of 358,100 shares. Market capitalization is $455.87M, with a 52-week range of USD 7.73–11.8 (NMS). Source: Nexqual, retrieved October 29, 2026 at 20:20 UTC.

Also available as compact Markdown for AI agents: nexqual.com/PRTA.md

Key facts (PRTA)

• Last four reported quarters (through Jun 30, 2026): revenue $54.5M, net income -$44.0M (-80.7% margin) (SEC filings).
• Insider open-market sales, last ~7 months: 2 Form 4 filings, $136K; 0 not under a Rule 10b5-1 plan ($0K); 0 by opportunistic insiders, 0 by routine insiders (three-year test, Cohen, Malloy & Pomorski 2012).
• Insider open-market purchases, last ~7 months: 15 Form 4 filings, $12.1M; 0 by opportunistic insiders, 0 by routine insiders.
• Analysts: Buy (mean 2.43 on a 1–5 scale) (7 analysts), mean target USD 21.4 (range 8–36).
• Total return with dividends: 1Y -15.3% vs S&P 500 +14.4%; 5Y -84.0% vs S&P 500 +79.1%.
• Next earnings: 2026-11-05, EPS estimate USD -0.3, revenue estimate $8.2M.

Financials (SEC 10-K; TTM = last four 10-Q/10-K quarters) (PRTA)

Fiscal years end Dec. EPS is split-adjusted.

Valuation (price ÷ last four quarters, through Jun 30, 2026) (PRTA)

P/S 8.4x · P/B 1.6x · Earnings yield -9.65%

Insider sales (SEC Form 4, open-market, last ~7 months) (PRTA)

2 of 2 under a Rule 10b5-1 trading plan (scheduled in advance). Unplanned sales were timed by the insider.

% of holdings sold = shares sold ÷ (shares sold + all holdings the insider reported on that Form 4, direct and through trusts).

Insider type follows Cohen, Malloy & Pomorski (Journal of Finance, 2012). An insider who traded the stock in the same calendar month in each of the past three years is a routine trader; one who traded in each of those years without such a pattern is an opportunistic trader. In their study, trades by opportunistic insiders predicted future returns and trades by routine insiders did not. Counts open-market purchases and sales only (SEC Form 4 codes P and S) by that insider in that company. Not investment advice.

Insider purchases (SEC Form 4, open-market, last ~7 months) (PRTA)

15 purchases, $12.1M. Private placements, offerings, dividend reinvestment and employee stock purchase plan buys are excluded.

Analysts (PRTA)

Consensus Buy (mean 2.43 on a 1–5 scale), 7 analysts; mean target USD 21.4 (low 8, high 36).

Total return (dividends reinvested) (PRTA)

PRTA earnings history and stock reaction

EPS as reported against the analyst consensus before the release; surprise uses the cent-rounded figures shown (in dollars when EPS and consensus have opposite signs). Stock reaction = close before the results to close after (the first close following a release after the bell or before the open).

PRTA recent SEC filings (last 120 days)

Source: SEC EDGAR. Quotes are the opening words of each item as filed; each form links to the filing. Insider Form 4 filings are listed in the insider sections.

PRTA revenue by product line (quarter ended Jun 30, 2026)

As tagged by the company in its SEC 10-Q / 10-K filings (XBRL).

PRTA suppliers, customers and competitors (named in its 10-K)

Quoted from the company's 10-K filed Feb 27, 2026.

PRTA company outlook (results filed Aug 6, 2026)

• “Roche is currently evaluating prasinezumab in the Phase 3 PARAISO trial, with primary completion expected in 2029," said Gene Kinney, Ph.D., President and Chief Executive Officer, Prothena. "In addition, Novo Nordisk is conducting the Phase 3 CLEOPATTRA clinical trial evaluating coramitug in patients with ATTR amyloidosis with cardiomyopathy, with primary completion expected in 2029.”
• “We also expect our partner Bristol Myers Squibb to complete the ongoing Phase 2 TargetTau-1 clinical trial evaluating moponetug (BMS-986446) in patients with early Alzheimer's disease in the first half of 2027.”

Quoted word-for-word from the SEC 8-K results press release.

PRTA analyst estimates and revisions

PRTA options: expected move

Options price a move of about ±15.2% (±$1.36) by Nov 20, 2026, which includes earnings on Nov 5, 2026. Over the last 8 reports the stock moved ±3.1% on average.

30-day implied volatility 61.5% vs 49.8% realized over the last 30 trading days. Put/call ratio (volume) 0. Cboe delayed quotes (15 min). Expected move = at-the-money straddle.

Key Statistics (as of October 29, 2026 at 20:20 UTC)

Technical Analysis (PRTA)

Nexqual's technical model rates PRTA "STRONG BUY" based on 5 bullish and 0 bearish signals across 127 daily candles, as of October 29, 2026 at 20:20 UTC.

Analyst Ratings (PRTA)

Wall Street analysts rate PRTA "Buy" based on 7 analysts, with a mean price target of USD 21.4 (range USD 8–36), per Nexqual as of October 29, 2026 at 20:20 UTC.

Earnings (PRTA)

Recent Earnings History

Source: Nexqual, October 29, 2026 at 20:20 UTC.

Financials & Fundamentals (PRTA)

Source: Nexqual, October 29, 2026 at 20:20 UTC.

Financial Health Score (PRTA)

Nexqual rates Prothena Corporation plc's overall financial health "Weak" across five dimensions, as of October 29, 2026 at 20:20 UTC.

Ownership (PRTA)

Source: Nexqual, October 29, 2026 at 20:20 UTC.

Leadership (PRTA)

Prothena Corporation plc is led by Gene G. Kinney, President, CEO & Director, per Nexqual as of October 29, 2026 at 20:20 UTC.

Major Backers & Investors (PRTA)

Notable institutional backers of Prothena Corporation plc include FMR, LLC, Rubric Capital Management LP, Fidelity, according to Nexqual as of October 29, 2026 at 20:20 UTC.

Active Investors

Index Funds (Passive)

Source: Nexqual, October 29, 2026 at 20:20 UTC.

From Prothena Corporation plc's Latest SEC 10-K Filing (filed 2026-02-27)

Key Strengths & Strategy (as disclosed to the SEC)

• Using our internally discovered CYTOPE® technology, we have developed an anti-pTDP-43 CYTOPE® that is designed to address the core molecular pathology associated with ALS in in the majority of cases.
• The goal of our approach is to slow the progressive neurodegenerative consequences of disease, a current unmet need.
• To demonstrate the potential of CYTOPE® we developed and investigated our TDP-43 CYTOPE® program in multiple preclinical models which was the basis of the scientific presentation.
• To address the growing prevalence of Alzheimer's disease with a therapeutic that can be made widely accessible to patients, we have developed highly potent anti-Aβ antibodies that retain or improve key attributes that are thought to underlie the observed efficacy of N-terminally directed therapeutics such as aducanumab, with the aim of offering similar or improved efficacy with convenient subcutaneous dosing regimens.

Partnerships

• Our collaboration with Roche to develop prasinezumab for the potential treatment of Parkinson's disease and other related synucleinopathies and the acquisition of our ATTR amyloidosis business by Novo Nordisk are examples of this, as are our two global licensing deals with BMS focused on neurodegenerative diseases.
• Our collaboration with Roche for the potential commercialization of prasinezumab is an example of this strategy, as is the acquisition of our ATTR amyloidosis business by Novo Nordisk.

Legal & Regulatory Risks (Item 1A, quoted)

• The FDA or other comparable foreign regulatory authorities may not accept data from trials conducted in locations outside of their jurisdiction.
• We are and may choose to conduct international clinical trials in the future.
• The policies of the FDA, the EMA, or other comparable regulatory authority may change and additional government regulations may be enacted that could prevent, limit or delay regulatory approval of our drug candidates.
• We deal with hazardous materials and must comply with environmental laws and regulations which can be expensive and restrict how we do business.

Source: SEC EDGAR 10-K, official filing. Curated by Nexqual.

Peers & Related Stocks

Data source: Nexqual — market data, technical indicators, analyst consensus, earnings, SEC EDGAR filings. Last updated: October 29, 2026 at 20:20 UTC. This page is informational and not investment advice.

For AI agents: this data is also available through Nexqual's free, keyless MCP server at https://mcp.nexqual.com/mcp; every result includes source_url, as_of and cite_as. More: nexqual.com/agents · llms.txt