Castle Biosciences
CSTL
186 hedge funds and large institutions have $678M invested in Castle Biosciences in 2026 Q1 according to their latest regulatory filings, with 30 funds opening new positions, 71 increasing their positions, 61 reducing their positions, and 36 closing their positions.
338% more call options, than puts
Call options by funds: $1.92M | Put options by funds: $437K
16% more repeat investments, than reductions
Existing positions increased: 71 | Existing positions reduced: 61
0.66% less ownership
Funds ownership: 93.52% → 92.86% (-0.66%)
4% less funds holding
Funds holding: 194 → 186 (-8)
17% less first-time investments, than exits
New positions opened: 30 | Existing positions closed: 36
36% less capital invested
Capital invested by funds: $1.06B → $678M (-$384M)
50% less funds holding in top 10
Funds holding in top 10: 2 → 1 (-1)
Top Buyers
| Rank | Fund | Capital Flow |
|---|---|---|
| 1 |
RI
RTW Investments
New York
|
+$21.1M |
| 2 |
Qube Research & Technologies (QRT)
London,
United Kingdom
|
+$10.6M |
| 3 |
Morgan Stanley
New York
|
+$7.38M |
| 4 |
SG Americas Securities
New York
|
+$7.32M |
| 5 |
Allianz Asset Management
Munich,
Germany
|
+$6.19M |
Top Sellers
| Rank | Fund | Capital Flow |
|---|---|---|
| 1 |
PCM
Portolan Capital Management
Boston,
Massachusetts
|
-$12.4M |
| 2 |
Wellington Management Group
Boston,
Massachusetts
|
-$8.5M |
| 3 |
Citadel Advisors
Miami,
Florida
|
-$8.04M |
| 4 |
B
Braidwell
Stamford,
Connecticut
|
-$6.89M |
| 5 |
Bank of America
Charlotte,
North Carolina
|
-$6.39M |
CSTL Hedge Fund Activity: Q1 2026 in Review
186 of the 8,126 institutional investors tracked by Wall St. Rank reported a position in Castle Biosciences (CSTL) for Q1 2026, worth a combined $678M — down 36% from $1.06B a quarter earlier.
Sellers outnumbered buyers: 36 funds closed out of CSTL and 30 opened new positions — a net loss of 6 holders — while 61 trimmed existing stakes and 71 added.
The largest buyer was RTW Investments, adding an estimated $21.1M. The largest seller was Portolan Capital Management, cutting an estimated $12.4M.
- 186 institutional investors held Castle Biosciences (CSTL) as of Q1 2026, down from 194 in Q4 2025.
- Funds reported $678M of Castle Biosciences stock for Q1 2026, down 36% quarter-over-quarter.
- 30 funds opened new Castle Biosciences positions in Q1 2026 and 36 closed out, a net change of -6 holders.
- The largest Castle Biosciences buyer in Q1 2026 was RTW Investments, an estimated $21.1M added.
- The largest Castle Biosciences seller in Q1 2026 was Portolan Capital Management, an estimated $12.4M sold.
Based on aggregated 13F filings for Q1 2026.