The 10% owner's open-market purchase is a modest bullish signal, but the small size relative to market cap limits its impact. Monitor for any subsequent filings (e.g., 8-K, press release) that might explain the insider's conviction, and watch for any additional insider buying or selling in the coming weeks to confirm the signal.
Price Chart
Executive Summary
William P. Scully, a 10% owner of Prothena, made a single-day open-market purchase of 37,500 shares for $323K on August 7, 2026, at $8.62 per share. This is a conviction buy from a major insider, representing 0.07% of the company's $459M market cap, which is a modest but notable signal given the insider's status and the lack of any recent insider selling at this level.
Key Financial Metrics
Key Facts
- 10% owner William P. Scully purchased 37,500 shares for $323,220 on August 7, 2026.
- The purchase was made at $8.62 per share, an open-market transaction.
- Total purchase value represents 0.07% of Prothena's $459M market cap.
- This is a single-insider conviction buy, not a cluster, but from a significant insider (10% owner).
Financial Impact
$323K insider purchase by 10% owner, representing 0.07% of market cap.
Risk Factors
- The purchase is small relative to market cap (0.07%), limiting its signaling power.
- Historical performance on PRTA shows a 44% win rate at T+20, suggesting past insider signals have been unreliable.
- The stock has a 67% bullish analyst consensus, which may already be priced in.
Market Snapshot
Investment Themes
Documents Analyzed
This report is based on 1 SEC document filed with EDGAR.
| Document | Accession Number |
|---|---|
| INSIDER-BUY Data (Synthetic) | 0001045463-26-000010 |
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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