$CSTL

$34.51 +$1.21 (3.63%) Close

$CSTL Overview Financial Statements SEC Filings Executives News Red Flags Capital Raising Ownership Insider Transactions Congressional Trades

Ownership

13F as of Q2 2026 · 30.5M shares outstanding

Who owns CSTL?

By type of holder

Institutions 89.7% Insiders 3.6% Everyone else 6.6%

Concentration Top 10 holders own 44.5%

BlackRock, Inc. 10.8% · RTW Investments, LP 9.1%

Institutional ownership

89.7%

-0.7 pts vs last qtr

Institutional holders

176

-10 vs last qtr

Net shares bought

−200.6K

by institutions in Q2 2026

New / sold out

23 / 33

positions opened vs closed

How is ownership changing?

Institutions, last 8 quarters

Biggest buyers in Q2 2026

Mackenzie Financial Corp +719.4K
Jefferies Financial Group Inc. NEW +647.4K

Biggest sellers in Q2 2026

Portolan Capital Management, LLC −1.0M
Eventide Asset Management, LLC SOLD OUT −386.4K

Who is planning to sell?

Notices of proposed sale, last 12 months

$19.4M

32 notices from 8 people

Shares covered

645.3K

2.11% of the company

Arranged in advance

84%

of the value is under a 10b5-1 plan

Under a 10b5-1 plan No plan

Largest proposed sellers

Derek Maetzold Officer 10b5-1 $11.4M
Tobin Juvenal Chief commercial officer 10b5-1 $2.82M

Every notice on Red Flags →

A Form 144 is notice of a planned sale, not the sale itself. What insiders actually sold is on Insider Transactions.

Is your stake being diluted?

Diluted share count, FY2018–FY2025

+1420.8%

+47.53% a year

Each share's claim on the business

−93.4%

shrank without buying or selling a share

Spent on buybacks vs paid in stock

— vs $215M

over 8 fiscal years

Diluted shares, split-adjusted

Buybacks Stock-based comp

How patient are the owners?

Institutional shares by how long they've been held

5+ years46% 3–5 years11% 1–3 years19% Under 1 year24%

Quarterly turnover

17.1%

of institutional shares changed hands

Top 10 managers, median time held

5 years

Super Investors

Investment managers reporting CSTL on Form 13F

Holder	Shares	% of company	Change vs last qtr	Held since	% of their book
B BlackRock, Inc.	3.3M	10.78%	+309.0K (+10.4%)	≤2021	0.0%
Shares held by quarter Peak holding3.3M (Q2'26) Change over 8 quarters+171.7K Share of the company10.780% BlackRock, Inc.'s full portfolio →
RI RTW Investments, LP	2.8M	9.09%	+20.0K (+0.7%)	Q4 '25	0.6%
Shares held by quarter Peak holding2.8M (Q2'26) Change over 8 quarters+2.8M Share of the company9.090% RTW Investments, LP's full portfolio →

BlackRock, Inc.

3.3M

% of company

10.78%

Change vs last qtr

+309.0K (+10.4%)

Held since

≤2021

RTW Investments, LP

2.8M

% of company

9.09%

Change vs last qtr

+20.0K (+0.7%)

Held since

Q4 '25

28 more super investors behind a free account

See every manager holding Castle Biosciences, Inc., how their position has changed, and how long they've held it.

Institutional Funds

Mutual funds and ETFs reporting CSTL on Form N-PORT; together they hold 35.3% of the company

Fund	Position value	Shares	% of company	% of the fund	As of
SA Strategic Advisers U.S. Total Stock Fund Fidelity Rutland Square Trust II	$26.2M	793.4K	2.60%	0.03%	August 31, 2026
VT Vanguard Total Stock Market Index Fund Vanguard Index Funds	$20.3M	852.7K	2.79%	0.00%	June 30, 2026

Strategic Advisers U.S. Total Stock Fund

Fidelity Rutland Square Trust II

Position value

$26.2M

% of company

2.60%

% of the fund

0.03%

As of

August 31, 2026

Vanguard Total Stock Market Index Fund

Vanguard Index Funds

Position value

$20.3M

% of company

2.79%

% of the fund

0.00%

As of

June 30, 2026

23 more funds behind a free account

See every fund holding Castle Biosciences, Inc. and how much of the fund the position is.

Insiders and 5%+ holders

From Forms 3/4/5 and Schedules 13D/G

Holder	Shares	% of company	Change vs last qtr	8 quarters	Held since	% of their book
MD Maetzold Derek J Insider	679.9K	2.23%	—	—	—	—
Insider holdings come from Form 3/4/5 filings, which are not quarterly. Share of the company2.230% Maetzold Derek J's insider activity →
OK Oelschlager Kristen M Insider	86.0K	0.28%	—	—	—	—
Insider holdings come from Form 3/4/5 filings, which are not quarterly. Share of the company0.280% Oelschlager Kristen M's insider activity →

Maetzold Derek J

Insider

679.9K

% of company

2.23%

Change vs last qtr

—

Held since

—

Oelschlager Kristen M

Insider

86.0K

% of company

0.28%

Change vs last qtr

—

Held since

—

9 more holders behind a free account

See every insider and 5%+ holder of Castle Biosciences, Inc..

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