The cluster of open-market purchases by a 10% owner at current levels signals strong insider conviction. Monitor for any upcoming corporate events (pipeline updates, regulatory milestones) that may have prompted the buying, and watch for additional insider filings or institutional accumulation.
Price Chart
Executive Summary
Prothena director and 10% owner William Scully purchased $819K in open-market shares on October 22, 2026, at $8.19 per share, outside a 10b5-1 plan. This follows his $404K purchase on October 23, bringing his two-day total to $1.22M. The insider buying cluster is significant relative to the company's $424M market cap (0.29% combined) and signals conviction from a major shareholder.
Key Financial Metrics
Key Facts
- William Scully, a 10% owner, purchased 100,000 shares at $8.19 for $819K on October 22, 2026.
- The purchase was an open-market transaction (Form 4 code P) with no 10b5-1 plan.
- Scully also bought 50,000 shares at $8.07 for $404K on October 23, 2026, for a two-day total of $1.22M.
- The combined $1.22M represents 0.29% of Prothena's $424M market cap.
- Recent insider activity (30 days) shows 9 buys totaling $7.1M, indicating sustained insider conviction.
- Institutional holders include Fidelity ($70M), Rubric Capital Management ($49M), and BlackRock ($48M).
Financial Impact
Insider purchase of $819K (0.19% of market cap) by a 10% owner, with no 10b5-1 plan.
Risk Factors
- Insider buying does not guarantee near-term stock performance; the stock may still face clinical or regulatory risks.
- The company is a biotech with no approved products, making it inherently volatile and dependent on pipeline success.
Market Snapshot
Investment Themes
Documents Analyzed
This report is based on 1 SEC document filed with EDGAR.
| Document | Accession Number |
|---|---|
| INSIDER-BUY Data (Synthetic) | 0001045463-26-000022 |
Filters
| Type | Now | ||||
|---|---|---|---|---|---|
Oct 26, 2026 1d ago | Insider Buy | $8.40 | awaiting T+1 | — | $8.40 (−0.00%) |
Oct 15, 2026 12d ago | Insider Buy | $8.35 $8.48 | ▲ +1.56% | ▲ +1.13% | $8.40 (+0.60%) |
Sep 30, 2026 27d ago | Insider Buy | $8.54 $8.36 | ▼ −2.11% | ▼ −2.85% | $8.40 (−1.64%) |
Sep 29, 2026 28d ago | Insider Buy | $8.38 $8.54 | ▲ +1.91% | ▲ +1.73% | $8.40 (+0.24%) |
Sep 21, 2026 5w ago | Insider Buy | $8.99 $8.68 | ▼ −3.45% | ▼ −2.73% | $8.40 (−6.56%) |
Sep 3, 2026 7w ago | Insider Buy | $9.82 $9.54 | ▼ −2.85% | ▼ −2.30% | $8.40 (−14.46%) |
Aug 21, 2026 9w ago | Insider Buy | $9.45 $9.39 | ▼ −0.63% | ▼ −0.34% | $8.40 (−11.11%) |
Aug 10, 2026 11w ago | Insider Buy | $9.12 $9.22 | ▲ +1.10% | ▲ +1.42% | $8.40 (−7.89%) |
Jul 30, 2026 12w ago | Insider Cluster | $8.12 $8.33 | ▲ +2.59% | ▲ +1.16% | $8.40 (+3.45%) |
Jun 18, 2026 18w ago | Insider Buy | $8.93 $9.15 | ▲ +2.46% | ▲ +2.78% | $8.40 (−5.94%) |
US Market Status
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