The concentrated buying by the 10% owner signals strong internal conviction. Traders should watch for upcoming clinical catalysts (e.g., trial readouts or regulatory updates) that may have motivated the purchases. Given the stock's recent weakness (down ~18% after a prior long call), this insider activity could indicate a near-term floor. Consider building a position on further dips but monitor for any negative news.
Price Chart
Executive Summary
10% owner William P. Scully purchased $1.49M of Prothena stock in two open-market transactions from June 4-11, 2026, at prices between $8.17 and $9.31. This represents ~0.34% of the $432M market cap and is a notable insider conviction signal, especially as prior insider buys in the last 30 days totaled $2.9M. The purchase comes amid a 67% analyst bullish consensus and adds to a pattern of insider buying.
Key Financial Metrics
Key Facts
- William P. Scully (10% owner) bought 175,000 shares total for $1.49M
- First trade: 50,000 shares at $9.31 on June 4; second: 125,000 shares at $8.17 on June 11
- Market cap of $432M makes this ~0.34% of company value
- Recent insider activity: 4 buys totaling $2.9M in the last 30 days
- Analyst consensus: 67% bullish (8 Buy, 3 Hold, 1 Sell)
Financial Impact
$1.49M insider purchase by 10% owner, ~0.34% of market cap
Risk Factors
- Prior model calls on PRTA have underperformed, with negative T+20 alpha on average
- Clinical-stage biotech binary risk: trial failures could erase gains
- Single insider buy, even by a 10% owner, may not be replicated by other executives
Market Snapshot
Investment Themes
Documents Analyzed
This report is based on 1 SEC document filed with EDGAR.
| Document | Accession Number |
|---|---|
| INSIDER-BUY Data (Synthetic) | 0001045463-26-000007 |
Filters
| Type | Now | ||||
|---|---|---|---|---|---|
Sep 3, 2026 28d ago | Insider Buy | $9.82 $8.86 | ▼ −9.78% | ▼ −8.57% | $8.44 (−14.05%) |
Aug 21, 2026 6w ago | Insider Buy | $9.45 $9.33 | ▼ −1.27% | ▼ −1.74% | $8.44 (−10.69%) |
Aug 10, 2026 7w ago | Insider Buy | $9.12 $8.88 | ▼ −2.63% | ▼ −2.58% | $8.44 (−7.46%) |
Jul 31, 2026 9w ago | Insider Cluster | $8.12 $8.76 | ▲ +7.88% | ▲ +4.37% | $8.44 (+3.94%) |
Jun 18, 2026 15w ago | Insider Buy | $8.93 $9.27 | ▲ +3.81% | ▲ +5.47% | $8.44 (−5.49%) |
Jun 12, 2026 15w ago | Insider Buy | $8.15 $9.15 | ▲ +12.27% | ▲ +13.65% | $8.44 (+3.56%) |
May 14, 2026 20w ago | 3 | $9.76 $9.83 | ▲ +0.72% | ▼ −0.25% | $8.44 (−13.52%) |
May 7, 2026 21w ago | 8-K | $10.73 $9.86 | ▼ −8.11% | ▼ −9.57% | $8.44 (−21.34%) |
Mar 27, 2026 26w ago | DEFA14A | $9.25 $10.36 | ▲ +12.00% | ▲ +7.70% | $8.44 (−8.76%) |
Mar 3, 2026 30w ago | EFFECT | $9.36 $9.77 | ▲ +4.38% | ▲ +4.86% | $8.44 (−9.83%) |
US Market Status
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