Prothena Corp Public
PRTA on Nasdaq. Pharmaceutical preparations. Market value $425m.
Price checks use the past 12 months to June 2026. Some use the latest annual report instead, as marked. Quality checks use five annual reports, the latest for the year to December 2025.
Cash flow or capital spending isn't reported, so free cash flow is unknown.
Should I look at this?
Not a fit for our list right now
Why it could be worth it
See Health care stocks that passed both tests
This is not advice. Check the numbers below.
We could not compute this from the filings.
The filings do not give us enough to work this out.
The filings do not give us enough to work this out.
Quality score: 60 of 100. Price score: 16 of 100. Our list needs 70 on quality and 60 on price.
$8.27 a share, 7% above its 1-year low
Over the past year the price has ranged from $7.73 to $11.80.
Pays no dividend
Prices from Monday’s close (5 October).
Five years of cash, in billions
| Revenue | |||||
| Revenue | $201m | $54m | $91m | $135m | $10m |
| Operating margin | |||||
| Operating margin | 35.9% | -244.1% | -209.1% | -114.4% | -2216.4% |
| Debt to equity | |||||
| Debt to equity | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Shares outstanding | |||||
| Shares outstanding | 0.05bn | 0.05bn | 0.05bn | 0.05bn | 0.05bn |
Health checks
- Free cash flow positiveNot enough data
- Accounting looks honest (Beneish)Not enough data
- Financial strength (Piotroski)1 of 8 checks we could run
- Profit backed by cash (accruals)No
- Debt0.00× equity
- Revenue growth, five yearsStrong, 62.6% a year
- Buying back its own sharesNo, 6% more shares since 2021
The quarter to June 2026
How the business did, compared with the same quarter a year earlier.
- Sales: $1 million last quarter, down 77% on a year ago.
- A loss of $19 million, compared with a loss of $126 million a year ago.
- It loses 102 cents on each $1 of sales, compared with 2723 cents a year earlier.
- 3% fewer shares than a year ago. Each share owns a bit more of the company.
- It has $288 million more cash than debt, down from $371 million a year ago.
- Sales grew on a year ago in 2 of the last 4 quarters.
| Quarter to | Amount |
|---|---|
| September 2024 | $970,000 |
| December 2024 | $2m |
| March 2025 | $3m |
| June 2025 | $4m |
| September 2025 | $2m |
| December 2025 | $21,000 |
| March 2026 | $51m |
| June 2026 | $1m |
| Quarter to | Amount |
|---|---|
| September 2024 | -$59m |
| December 2024 | -$58m |
| March 2025 | -$60m |
| June 2025 | -$126m |
| September 2025 | -$37m |
| December 2025 | -$22m |
| March 2026 | $33m |
| June 2026 | -$19m |
From the company's quarterly reports to the SEC.
Dates
- Next results (estimated)
- n/a
- Last annual report (10-K)
- 27 February 2026
- Next quarterly (estimated, 10-Q)
- 5 November 2026
Who owns it
None of the long-term investors we follow own it. 188 funds in all.
Largest holders overall
- FMR$70mCut
- Rubric Capital Management LP$49m
- BlackRock$48mAdded
- State Street$23mAdded
- Acadian Asset Management$20mAdded
- Vanguard Portfolio Management$16mAdded
- D. E. Shaw$16mCut
- ADAR1 Capital Management$15m
- TWO Sigma Investments, LP$12mAdded
- Palo Alto Investors LP$11mCut
From 13F filings for the quarter ended 30 June 2026.
Big holders and activists
7 investors own more than 5%.
- FMR LLCPassive investorat least 13.8%(filed with 1 related holder)Since 30 June 2026
- SCULLY WILLIAM PPassive investor10.3%+0.5 ptsSince 7 May 2026
- Fennell Todd W.Passive investor10.2%+0.4 ptsSince 18 August 2026
- Wellington Management Company LLPPassive investor9.5%Since 31 December 2024
- Rubric Capital Management LPPassive investorat least 9.3%+2.5 pts(filed with 1 related holder)Since 31 March 2026
- BlackRock, Inc.Passive investor6.9%+1.2 ptsSince 30 June 2026
- ADAR1 Capital Management, LLCPassive investorat least 2.7%−3.6 pts(filed with 2 related holders)Since 30 September 2025
- Wellington Management Group LLPPassive investorSold down below 5%Since 30 May 2025
- T. Rowe Price Associates, Inc.Passive investorSold down below 5%Since 30 June 2025
- Logos Global Management LPPassive investorSold down below 5%Since 30 June 2025
- EcoR1 Capital, LLCPassive investorSold down below 5%Since 27 May 2025
What they said
The reporting persons acquired Ordinary Shares for investment purposes based on their belief that the Issuer's Ordinary Shares, when purchased, was undervalued and represented an attractive investment opportunity. The reporting persons will routinely monitor the Issuer regarding…
Read the filing
| Holder | Stake | Since | |
|---|---|---|---|
FMR LLC Passive investor | at least 13.8% (filed with 1 related holder) | 30 June 2026 | |
SCULLY WILLIAM P Passive investor | 10.3%+0.5 pts | 7 May 2026 | |
Fennell Todd W. Passive investor | 10.2%+0.4 pts | 18 August 2026 | |
Wellington Management Company LLP Passive investor | 9.5% | 31 December 2024 | |
Rubric Capital Management LP Passive investor | at least 9.3%+2.5 pts (filed with 1 related holder) | 31 March 2026 | |
BlackRock, Inc. Passive investor | 6.9%+1.2 pts | 30 June 2026 | |
ADAR1 Capital Management, LLC Passive investor | at least 2.7%−3.6 pts (filed with 2 related holders) | 30 September 2025 | |
Wellington Management Group LLP Passive investor | Sold down below 5% | 30 May 2025 | |
T. Rowe Price Associates, Inc. Passive investor | Sold down below 5% | 30 June 2025 | |
Logos Global Management LP Passive investor | Sold down below 5% | 30 June 2025 | |
EcoR1 Capital, LLC Passive investor | Sold down below 5% | 27 May 2025 | What they saidThe reporting persons acquired Ordinary Shares for investment purposes based on their belief that the Issuer's Ordinary Shares, when purchased, was undervalued and represented an attractive investment opportunity. The reporting persons will routinely monitor the Issuer regarding… Read the filing |
From Schedule 13D and 13G filings: anyone owning more than 5% must file one.
What insiders did
No insider bought shares on the open market in the last 12 months. 2 sold $135,975, $135,975 of it under preset trading plans.
- Kingston Anne EvansChief Strategy OfficerSoldunder a preset trading plan
- Date
- 29 July 2026
- Shares
- 7,662
- Price
- $8.47
- Value
- $64,919
- Isaacs Michael JohnGeneral Counsel & Company Sec.Soldunder a preset trading plan
- Date
- 29 July 2026
- Shares
- 8,386
- Price
- $8.47
- Value
- $71,055
| Date | Who | Did | Shares | Price | Value |
|---|---|---|---|---|---|
| 29 July 2026 | Kingston Anne Evans Chief Strategy Officer | Sold under a preset trading plan | 7,662 | $8.47 | $64,919 |
| 29 July 2026 | Isaacs Michael John General Counsel & Company Sec. | Sold under a preset trading plan | 8,386 | $8.47 | $71,055 |
From Form 4 filings: insiders must report trades in their own company's shares within two days.
Warning signs in its filings
Problems the company itself reported to the SEC, in its own words.
None of the warning signs we check for were found.
We look for five warning signs: doubt it can keep going, weak checks on its own accounts, a notice that its past accounts can't be relied on, a change of auditor, and one customer bringing in a big share of sales. We don't check lawsuits, investigations or debt yet.
We checked the auditor's report, internal controls, restatement notices, auditor changes and big customers in the 10-K filed 27 Feb 2026, plus the 10-Q filed 6 Aug 2026 and 4 later 8-Ks.
A 10-K is the yearly report every US company files with the SEC. An 8-K is a short notice of a big event.
What could go wrong
Cheap for a reason is the question the numbers cannot answer.
Whether the price already reflects the risks is what the deep dive is for.
The deep dive
Everything above is arithmetic on public filings. The deep dive reads the last ten years of annual reports, the proxy statements, and the earnings calls, then argues the case the way Buffett, Klarman, and Hohn would, and checks every claim against the source.
- What the business is worth, as a range, and the margin of safety at today’s price
- Prices to start buying, buy, and buy hard
- The three things that would make this a mistake
- Every number footnoted to the filing it came from
Your first deep dive is free.
Not advice. Numbers on this page come from SEC filings and are updated each night; prices are updated again after the US market closes. The five-year figures are rounded.