Insider Buy ·Filed Sep 21, 2026
Insider cluster: 1 insiders, $843K total
Actionable Insight ▲ Bullish
A $843K open-market buy by a 10% owner is a strong insider conviction signal. Monitor for any upcoming corporate events (pipeline updates, partnership news) that may have prompted this purchase, as well as any follow-on buying by other insiders.
Latest settled — T+20d
PRTA ▼ -5.45% at T+20d
LONG call ✗ call lost -5.45% · α vs SPY -4.89% · entry $8.99 → $8.50
Latest observation: T+23 -6.94% FF3 residual α
T+1d
-3.45%
call -3.45% · α -2.73%
$8.68
settled 5w ago
T+5d
-2.34%
call -2.34% · α -1.15%
$8.78
settled 28d ago
T+20d
-5.45%
call -5.45% · α -4.89%
$8.50
settled 7d ago
T+60d
Pending
in 7w
Price Chart
Loading chart...
Executive Summary
10% owner William P. Scully purchased $843K of Prothena (PRTA) stock on the open market at $8.43/share on September 18, 2026. This is a large, conviction insider buy from a significant shareholder, representing a strong bullish signal.
Key Financial Metrics
Direction
buying
Total Value
$843.0K
Insiders
1
Key Facts
- 10% owner William P. Scully bought 100,000 shares at $8.43 for a total of $843,000
- Purchase was an open-market transaction (code P), not part of a 10b5-1 plan
- Single insider conviction buy of substantial dollar value
Financial Impact
$843,000 open-market purchase by a 10% owner
insider ownership
Risk Factors
- Biotech stock with binary pipeline risk — insider buy does not guarantee clinical success
Investment Themes
Documents Analyzed
This report is based on 1 SEC document filed with EDGAR.
| Document | Accession Number |
|---|---|
| INSIDER-BUY Data (Synthetic) | 0001045463-26-000016 |
15 reports for PRTA
63% Hit rate @ T+1 Went positive at some point 6 of 8 best @ T+60▲ +14.11%
Filters
Rows
| Type | Now | ||||
|---|---|---|---|---|---|
Oct 26, 2026 1d ago | Insider Buy | $8.40 | awaiting T+1 | — | $8.81 (+4.88%) |
Oct 15, 2026 12d ago | Insider Buy | $8.35 $8.48 | ▲ +1.56% | ▲ +1.13% | $8.81 (+5.51%) |
Sep 30, 2026 27d ago | Insider Buy | $8.54 $8.36 | ▼ −2.11% | ▼ −2.85% | $8.81 (+3.16%) |
Sep 29, 2026 28d ago | Insider Buy | $8.38 $8.54 | ▲ +1.91% | ▲ +1.73% | $8.81 (+5.13%) |
Sep 21, 2026 5w ago | Insider Buy | $8.99 $8.68 | ▼ −3.45% | ▼ −2.73% | $8.81 (−2.00%) |
Sep 3, 2026 7w ago | Insider Buy | $9.82 $9.54 | ▼ −2.85% | ▼ −2.30% | $8.81 (−10.29%) |
Aug 21, 2026 9w ago | Insider Buy | $9.45 $9.39 | ▼ −0.63% | ▼ −0.34% | $8.81 (−6.77%) |
Aug 10, 2026 11w ago | Insider Buy | $9.12 $9.22 | ▲ +1.10% | ▲ +1.42% | $8.81 (−3.40%) |
Jul 30, 2026 12w ago | Insider Cluster | $8.12 $8.33 | ▲ +2.59% | ▲ +1.16% | $8.81 (+8.50%) |
Jun 18, 2026 18w ago | Insider Buy | $8.93 $9.15 | ▲ +2.46% | ▲ +2.78% | $8.81 (−1.34%) |
Showing 10 of 15
US Market Status
Market Closed — Opens Wed (< 1m)
Subscribe to SecBot
Get Real-Time SEC Filing Intelligence
Comprehensive SEC filing analysis delivered the moment filings hit EDGAR. Sentiment scoring, impact analysis, and actionable insights for every material event.
Create a free account Live analysis, Telegram alerts, watchlists and the MCP server for subscribers