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Prothena CORP Public Ltd Co Stock: price and insider trades · United States
1 insider bought €6.8M of shares over the last 90 days, the latest filed 15 Oct 2026.
Prothena CORP Public Ltd Co: what insiders have been doing
Prothena CORP Public Ltd Co, classified in the Healthcare & Pharma sector, is a listed company. Its insiders report their share dealings to SEC (Form 4). The last twelve months, up to 18 October 2026, brought 35 filings signed by 12 insiders.
Purchases and sales both appear in the filings: 12 purchases (1 insider, €6.8M) and 2 sales (2 insiders, €119k). Taken together, the purchases exceed the sales by €6.7M. Open-market purchases are the filings investors watch most closely, because the insider pays for the shares out of pocket. The buyers include 1 major shareholder. Scully William P filed the largest purchase, €1.2M, on 30 September 2026, which represents 0.31% of the company's market value.
The most recent open-market purchase was published on 15 October 2026, 3 days ago. Filings reach the SEC (Form 4) feed a median of 2 days after the trade. The legal deadline for a Form 4 is two business days after the transaction.
With 35 filings in twelve months, the company is more active than the median of 22 filings across the 5,458 companies we follow on the same exchange. Over the whole record (from 2016), the tally stands at 14 purchases and 10 sales. For the fiscal year to 31 December 2025, the annual 10-K puts revenue at 9.7 m USD and net income at -244.1 m USD.
For comparison within the same sector, see the insider buying recorded at Anixa Biosciences Inc and Vivos Inc. This summary is built from SEC (Form 4) disclosures alone and does not predict where the share price will go.
Insider Decl.
158
Thresholds
n/a
Buy Volume
€46M
14 ops. · all time
Sell Volume
€25M
10 ops. · all time
Who traded when
BuySaleWilliam P. Scully12 buys
Anne Evans Kingston1 sale
EcoR1 Capital, LLC1 sale
Michael John Isaacs1 sale
Since the insiders bought
- -13.2%Entry US$9.54 · Close 16 Oct 2026 US$8.28
- +178.6%Entry US$26.97 · Close at T+365 US$75.15
Entry is the close on the day after publication, the first price a reader could act on. Prices in the listing currency. Past moves are not a forecast.
This score ranks the purchase within its own market. A position size is suggested only on the venues of the backtested strategy universe; elsewhere, signals stay on watch. Not investment advice.
Financial data
as of FY 2025FY ended December 2025 · cache
US$8.78
Analyst consensus
5 analysts2.50/5
US$8.00Target US$21.40(+144%)US$36.00
Income statement
RevenueUS$9.7M
EBITDA-US$183.7M-1897% margin
Net income-US$244.1M-80.7% margin
Valuation
PER (forward)-5.8x
P/Book1.6x
Beta-0.33
Balance sheet & cash
Market capUS$450.7M
Total debtUS$8.4M
Free Cash Flow-US$163.7M
Debt / Equity2%
Profitability & ownership
ROE-14.4%
ROA-10.7%
% insiders22.2%
% institutions93.9%
Last declaration on 15 October 2026
Declarations158 total
100,000 shares@ US$8.35480.19% mcap10.9% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000021:0
Canonical exit: 11 Jan 2027 (T+90)
10,000 shares@ US$8.45690.019% mcap1.1% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000021:1
Canonical exit: 12 Jan 2027 (T+90)
125,000 shares@ US$8.40120.23% mcap15.5% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000020:0
Canonical exit: 5 Jan 2027 (T+90)
90,000 shares@ US$8.56560.17% mcap11.4% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000020:1
Canonical exit: 6 Jan 2027 (T+90)
100,000 shares@ US$8.57240.19% mcap17.4% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000019:0
Canonical exit: 31 Dec 2026 (T+90)
162,000 shares@ US$8.6770.31% mcap34.1% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000018:0
Canonical exit: 28 Dec 2026 (T+90)
103,500 shares@ US$8.59780.21% mcap32.6% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000017:0
Canonical exit: 27 Dec 2026 (T+90)
100,000 shares@ US$8.43460.20% mcap45.6% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000016:0
Canonical exit: 17 Dec 2026 (T+90)
27,000 shares@ US$9.47180.059% mcap13.7% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000015:0
Canonical exit: 1 Dec 2026 (T+90)
50,000 shares@ US$8.78860.10% mcap23.3% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000014:0
Canonical exit: 18 Nov 2026 (T+90)
336,000 shares0Ordinary Shares, par value $0.01 per shareSEC:0001045463-26-000013:0
627,553 shares0Ordinary Shares, par value $0.01 per shareSEC:0001045463-26-000013:1
251,553 shares0Ordinary Shares, par value $0.01 per shareSEC:0001045463-26-000011:0
34,000 shares@ US$8.61920.068% mcap15.8% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000010:0
Canonical exit: 5 Nov 2026 (T+90)
3,500 shares@ US$8.61920.0070% mcap1.6% of flowOrdinary Shares, par value $0.01 per shareSEC:0001045463-26-000010:1
Canonical exit: 5 Nov 2026 (T+90)
4,694 shares@ US$8.560.0094% mcap36.1% of flowOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003409:0
51,000 shares@ US$8.560.10% mcap33.5% of flowOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003417:1
84,000 sharesOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003412:0
57,000 sharesOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003413:0
15,000 sharesOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003416:0
78,000 sharesOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003414:0
51,000 sharesOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003415:0
51,000 sharesOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003417:0
8,386 shares@ US$8.47310.017% mcap63.9% of flowOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003409:1
3,498 shares@ US$8.560.0070% mcap31.6% of flowOrdinary Shares, par value $0.01 per shareSEC:0000905148-26-003410:0
25 of 158 declarations
About Prothena CORP Public Ltd Co
Prothena Corporation plc (ticker PRTA) is a United States–listed biotechnology company trading on the NASDAQ market, with operational headquarters in Brisbane, California. The company is a late-stage clinical biopharmaceutical developer focused on protein dysregulation and misfolded-protein biology. Its investment case is built on the possibility of developing disease-modifying therapies for severe, underserved neurodegenerative disorders and rare peripheral amyloid diseases. ([sec.gov](https://www.sec.gov/Archives/edgar/data/1559053/000155905326000008/prta-20251231.htm?utm_source=openai))
Prothena was formed in 2012 as an Irish public limited company, and its ordinary shares began trading on the Nasdaq Global Market on December 21, 2012. The stock now trades on the Nasdaq Global Select Market. This structure gives the company an Irish corporate domicile while maintaining a clearly U.S.-centered operating footprint, which is common among biotech companies seeking access to U.S. capital markets and scientific talent in California. ([sec.gov](https://www.sec.gov/Archives/edgar/data/1559053/000155905326000008/prta-20251231.htm?utm_source=openai))
Read moreShow less
From an operating perspective, Prothena is a development-stage company rather than a commercial-stage drug manufacturer. Its pipeline includes wholly owned and partnered programs across Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and other neurodegenerative conditions, alongside rare amyloid disorders. A key element of its platform is CYTOPE®, Prothena’s proprietary technology designed to target a broad range of intracellular disease pathways in the brain and periphery. Because the company does not yet have marketed products, its long-term valuation depends primarily on clinical execution, partnering economics, and the ability to progress assets through proof-of-concept and later-stage studies. ([sec.gov](https://www.sec.gov/Archives/edgar/data/1559053/000155905326000008/prta-20251231.htm?utm_source=openai))
Competitively, Prothena occupies a specialist niche rather than competing on scale. Its differentiation lies in deep scientific expertise around protein misfolding, amyloid biology, and neurodegenerative mechanisms. Among the best-known programs are coramitug, formerly PRX004, for ATTR amyloidosis with cardiomyopathy; PRX012 and PRX123 for Alzheimer’s disease; and other neurology-focused assets. The company also retains strategic collaborations with major pharmaceutical partners such as Novo Nordisk and Bristol Myers Squibb, creating a pathway to milestone receipts and shared development risk. ([ir.prothena.com](https://ir.prothena.com/investors/press-releases/news-details/2026/Prothena-Reports-Fourth-Quarter-and-Full-Year-2025-Financial-Results-and-Provides-Financial-Guidance-and-Business-Highlights/default.aspx?utm_source=openai))
Recent news has highlighted a stronger focus on capital discipline. In 2025, Prothena announced a major corporate restructuring, including a substantial workforce reduction, to lower operating costs and concentrate resources on remaining wholly owned and partnered programs. In early 2026, the company reported cash, cash equivalents and restricted cash of $308.4 million with no debt, and it authorized a share repurchase plan of up to $100 million. It also disclosed meaningful development progress, including a U.S. FDA Fast Track designation for Novo Nordisk’s coramitug program and a $50 million milestone payment tied to the ongoing Phase 3 CLEOPATTRA study. For international investors, PRTA remains a high-risk, high-upside biotech story driven by clinical readouts, partnership milestones, and pipeline optionality rather than current product revenues. ([ir.prothena.com](https://ir.prothena.com/investors/press-releases/news-details/2025/Prothena-Announces-Corporate-Restructuring/default.aspx?utm_source=openai))
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