Stocks › Diagnostics & Research › CSTL

Castle Biosciences CSTL

US equityMarket cap rank #3235Diagnostics & Research

$33.00 −$0.36 (-1.08%)

Market closed · Oct 8, 7:00 am ET · Last extended-hours $33.00 0.00%

Open$33.15

Prev close$33.36

Day range$32.77 – $33.72

Volume351.5K

Market cap$1.01B

P/E (TTM)–

Dividend yield–

Ownership & positioning

Who holds it, who is betting against it, and where the big money is moving

Institutional ownership90.7%-1.26 pts vs. prior quarter

Institutions holding216-1 vs. prior quarter

Insider trades (recent)13 buys / 37 sellsNet selling

Short interest6.22% of floatDays to cover 7.4 · as of 15 Sep 2026

Short-sale volume share16.6%5-day average of daily volume

Short-sale volume as % of daily volume

Large-order net flow, last 20 sessions

Net of large-order buying minus selling, in USD. Over this window: +$1.27M (15 inflow days, 5 outflow days).

Net flow by order size, last 20 sessions

Super/Big orders approximate institutional-size trades; Mid/Small approximate retail-size trades. Net buy minus sell value in each bucket, summed over the window.

The five largest holders on file together own 33.2% of shares outstanding.

Largest holders

BlackRock10.78%
RTW Investments, LP9.09%
Principal Global Investors, LLC5.65%
Vanguard Capital Management, LLC4.66%
Acadian Asset Management LLC3.01%
Allianz Asset Management AG2.88%
Vanguard Portfolio Management, LLC2.75%
Summit Partners Public Asset Management, LLC2.70%

By investor type

Mutual Fund61.16%
Hedge Fund22.15%
Public Company4.32%
Individual/Insider2.02%
Private Company1.07%
Government Pension Fund1.03%
Insurance Company0.74%
Sovereign Wealth Fund0.21%

Reported short interest has risen from 4.92% to 6.22% of float over the last 6 biweekly reports (30 Jun 2026 to 15 Sep 2026).

Recent institutional activity

Holder	Type	Period	Share change	New stake
Mackenzie Financial Corporation	Mutual Fund	2026/Q3	+719,396	2.6%
Jefferies Financial Group Inc.	Public Company	2026/Q3	+647,391	2.1%
Acadian Asset Management LLC	Mutual Fund	2026/Q3	+434,227	3.0%
Point72 Asset Management, L.P.	Hedge Fund	2026/Q3	+357,317	1.2%
Kennedy Capital Management LLC	Mutual Fund	2026/Q3	+348,371	1.1%
BlackRock	Mutual Fund	2026/Q3	+309,017	10.8%
Citadel Advisors LLC	Hedge Fund	2026/Q3	+144,376	0.9%
First Trust Advisors L.P.	Mutual Fund	2026/Q3	+137,128	0.5%
Allspring Global Investments, LLC	Mutual Fund	2026/Q3	+131,807	1.0%
AQR Capital Management	Hedge Fund	2026/Q3	+102,204	0.5%
Hudson River Trading LLC	Private Company	2026/Q3	+99,995	0.4%
PanAgora Asset Management, Inc.	Mutual Fund	2026/Q3	+78,687	1.0%
Trexquant Investment LP	Hedge Fund	2026/Q3	+75,677	0.7%
Allianz Asset Management AG	Mutual Fund	2026/Q3	+67,934	2.9%
Geode Capital Management, LLC	Mutual Fund	2026/Q3	+67,812	2.6%

Institutional buy/sell activity by reporting period, largest moves first.

Insider transactions

Date	Insider	Title	Transaction	Shares	Price	Held after
4 Oct 2026	Derek Maetzold	Chief Executive Officer	Intent to Sell (Form 144)	-28,992	$36.65	–
30 Sep 2026	Kristen Oelschlager	Chief Operating Officer	Derivative Exercise and Sale	-4,153	$36.38	86,005
29 Sep 2026	Tobin Juvenal	Chief Commercial Officer	Automatic Disposition	-6,577	$35.50	52,007
20 Sep 2026	Derek Maetzold	Chief Executive Officer	Automatic Disposition	-5,916	$35.33	191,265
20 Sep 2026	Derek Maetzold	Chief Executive Officer	Derivative Exercise and Sale	-8,580	$35.33	191,265
14 Sep 2026	Tobin Juvenal	Chief Commercial Officer	Automatic Disposition	-6,600	$35.14	58,584
10 Sep 2026	Derek Maetzold	Chief Executive Officer	Automatic Disposition	-5,934	$32.78	197,181
10 Sep 2026	Derek Maetzold	Chief Executive Officer	Derivative Exercise and Sale	-8,584	$32.00	197,181
31 Aug 2026	Kristen Oelschlager	Chief Operating Officer	Derivative Exercise and Sale	-4,152	$34.02	86,005
30 Aug 2026	Tobin Juvenal	Chief Commercial Officer	Automatic Disposition	-1,730	$32.81	65,184
27 Aug 2026	Derek Maetzold	Chief Executive Officer	Automatic Disposition	-6,132	$33.88	203,115
27 Aug 2026	Derek Maetzold	Chief Executive Officer	Derivative Exercise and Sale	-12,428	$33.14	203,115
24 Aug 2026	Tobin Juvenal	Chief Commercial Officer	Automatic Disposition	-9,050	$35.04	66,914
24 Aug 2026	Kristen Oelschlager	Chief Operating Officer	Open Market Disposition	-24,602	$34.64	85,937
16 Aug 2026	Tobin Juvenal	Chief Commercial Officer	Automatic Disposition	-1,730	$29.59	75,964
13 Aug 2026	Derek Maetzold	Chief Executive Officer	Automatic Disposition	-6,132	$30.02	209,247
13 Aug 2026	Derek Maetzold	Chief Executive Officer	Derivative Exercise and Sale	-1,100	$30.02	209,247
13 Aug 2026	Frank Stokes	Chief Financial Officer	Open Market Disposition	-24,908	$29.77	35,177
4 Aug 2026	Derek Maetzold	Chief Executive Officer	Automatic Disposition	-16,114	$31.34	215,379
4 Aug 2026	Derek Maetzold	Chief Executive Officer	Derivative Exercise and Sale	-22,902	$31.34	215,379

From Form 4/Form 144 filings. Negative share counts are disposals (sales, gifts, or shares withheld for taxes); positive are acquisitions.

Short interest, by report

Report date	Shares short	% of float	Days to cover
15 Sep 2026	1,899,369	6.2%	7.4
31 Aug 2026	1,976,754	6.5%	5.1
14 Aug 2026	1,753,605	5.7%	3.7
31 Jul 2026	1,561,988	5.1%	3.2
15 Jul 2026	1,421,793	4.7%	5.7
30 Jun 2026	1,491,750	4.9%	3.2

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