Castle Biosciences, Inc.
Castle Biosciences, Inc. (CSTL) Stock Ownership
Institutional vs insider vs public ownership from 13F and float data — top holders, activity, and insider trades below.
SEC 13F · FMP · CSTL · as of Sep 30, 2025
Ownership Breakdown
177
Institutional Holders
▲ 25 vs Q2
$608.33M
Total Inst. Value
▲ $66.53M vs Q2
30.33M
Shares Outstanding
freeFloat 88.25%
26.65M
13F Shares Held
▲ 112,593 vs Q2
Institutional ownership = 13F shares ÷ total outstanding. Insider % = 100 − free float. Public % = free float − institution %. Data: FMP /symbol-positions-summary + /shares-float + SEC EDGAR.
Top Institutional Holders
CSTL largest shareholders · institutional ownership
Q3 2025 · SEC 13F
Showing top 10 holders
| Holder | Shares | % Owned | Weight | Value | Reported | Change |
|---|---|---|---|---|---|---|
BLACKROCK, INC. services-medical laboratories | 3.19M | 11.03% | 11.03% | $72.63B | Nov 12, 2025 | ▲ 35.2K |
VANGUARD GROUP INC services-medical laboratories | 2.17M | 7.51% | 7.51% | $49.46B | Nov 7, 2025 | ▲ 2.3K |
PRINCIPAL FINANCIAL GROUP INC services-medical laboratories | 1.79M | 6.21% | 6.21% | $40.86B | Nov 4, 2025 | ▼ 4.6K |
PORTOLAN CAPITAL MANAGEMENT, LLC services-medical laboratories | 1.52M | 5.24% | 5.24% | $34.50B | Nov 13, 2025 | ▲ 25.5K |
DIMENSIONAL FUND ADVISORS LP services-medical laboratories | 1.47M | 5.10% | 5.10% | $33.56B | Nov 12, 2025 | ▲ 96.1K |
NUVEEN, LLC services-medical laboratories | 957.1K | 3.31% | 3.31% | $21.79B | Nov 12, 2025 | ▼ 116.0K |
BRAIDWELL LP services-medical laboratories | 822.7K | 2.85% | 2.85% | $18.73B | Nov 14, 2025 | — held |
STATE STREET CORP services-medical laboratories | 724.1K | 2.50% | 2.50% | $16.49B | Nov 14, 2025 | ▲ 16.4K |
AIGH CAPITAL MANAGEMENT LLC services-medical laboratories | 707.3K | 2.45% | 2.45% | $16.10B | Oct 31, 2025 | NEW |
GEODE CAPITAL MANAGEMENT, LLC services-medical laboratories | 698.6K | 2.42% | 2.42% | $15.91B | Nov 12, 2025 | ▲ 8.7K |
Data from SEC Form 13F filings. Ownership bar normalised to largest holder. Change flags: isNew / isSoldOut / changeInSharesNumber (FMP extract-analytics/holder).
Institutional Activity
Q3 2025 vs prior quarter
Q3 2025
27
Increased
+1.67M shares3
New Positions
first time holders17
Decreased
−2.05M shares0
Sold Out
fully exitedNet shares change (top 50)
387.3K
+1.67M / −2.05M
Net new holders
+13
3 new / 0 exited
Based on top 50 institutional holders by position size. Fields: isNew, isSoldOut, changeInSharesNumber (FMP extract-analytics/holder, limit=50).
Insider Buying vs Selling
CSTL insider trading · insider activity
Source: SEC Form 4
5
Buy transactions
29
Sell transactions
0.17
Buy/Sell ratio
$0M
Total disposed
Recent Insider Transactions
Showing 10 most recent · Common Stock only
| Name · Role | Date | Type | Shares | Price | Value | After Trans. | Filing |
|---|---|---|---|---|---|---|---|
Olson Tiffany director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
Goldberg Ellen director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
Harrison Miles director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
Cotton Rodney director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
Caple Kim director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
BRADBURY DANIEL director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
Cole G Bradley director | May 28, 2026 | Award | 11,766 | — | — | 11.8K | Form 4 ↗ |
Source: /insider-trading/search (FMP stable). Buy/Sell direction: acquisitionOrDisposition A=Buy, D=Sell. RSU vesting (M-Exempt) excluded from sentiment bar. All data from SEC EDGAR public filings.
About institutional & insider ownership
Castle Biosciences, Inc. (CSTL) is primarily owned by institutional investors, who hold approximately 87.9% of total shares outstanding. Company insiders own approximately 11.75%, while retail and public investors account for the remaining 0.39%.
The largest institutional shareholder of Castle Biosciences, Inc. is BLACKROCK, INC., holding approximately 3.19 million shares — equal to 11.03% of outstanding shares — as of September 30, 2025.
A total of 177 institutional investors currently hold CSTL stock, with a combined institutional value of approximately $608,334,866 as of the most recent 13F filing period.
Frequently asked questions
CSTL ownershipCastle Biosciences, Inc. (CSTL) is primarily owned by institutional investors, who hold approximately 87.9% of shares. The largest shareholder is BLACKROCK, INC. with a 11.03% stake. Company insiders hold 11.75%. Data sourced from SEC Form 13F as of September 30, 2025.