Castle Biosciences, Inc. (CSTL) Institutional Ownership
Q1 2026 13F Data|Updated 2026-06-13
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Institutional ownership decreased this quarter (-61.85 pp), while top 10 holders maintain a highly concentrated 54.4% of value.
Institutional Ownership104.0%$653M total value · ▼ 61.85 pp vs prior quarter
Can exceed 100% due to securities lending, short interest, and reporting timing differences.
Smart Money Score39 / 100Bearish
Based on ownership concentration, fund quality, buying/selling activity, conviction signals, and institutional trend.
Institutions & Flow183 holders-9 net flow (+30 / -39)
AI Insights & Key Takeaways
- Negative Institutional Flow (-9)
- Renaissance Technologies Llc and Millennium Management Llc maintain significant positions
- Top 10 holders control 54.4% of institutional value
- No Insider Signal
Top Institutional Holders of CSTL
Ranked by reported Q1 2026 13F market value
Top 10 Holders
54.4%
Top 25 Holders
79.3%
Share of total reported institutional value in CSTL held by the largest 10 / 25 filers.
| # | Institution | Shares Held | Market Value | QoQ Change | Ownership % | % of Fund |
|---|---|---|---|---|---|---|
| 1 | BlackRock, Inc. | 3.0M | $73.2M | -3.9% | 9.835% | 0.00% |
| 2 | RTW INVESTMENTS, LP | 2.8M | $67.7M | +30.4% | 9.094% | 0.67% |
| 3 | PRINCIPAL FINANCIAL GROUP INC | 1.8M | $43.5M | -2.1% | 5.835% | 0.02% |
Quarterly Institutional Activity
Filings activity in CSTL during Q1 2026, grouped by how each filer changed its position.
CSTL Institutional Ownership by Quarter
8 quarters of 13F filings · Δ columns show change vs prior quarter
| Quarter | Inst. Holders | Δ Holders | Ownership % | Δ Ownership | Total 13F Value | Δ Value |
|---|---|---|---|---|---|---|
| Q1 2026 | 183 | 4.7% | 104.03% | 61.85 pp | $653M | 37% |
| Q4 2025 | 192 | +13% | 165.88% | +71.86 pp | $1.04B | +76% |
| Q3 2025 | 170 | +11% | 94.02% | +11.46 pp | $590M | +14% |
| Q2 2025 | 153 | 15% | 82.56% | +5.65 pp | $518M | +7.3% |
| Q1 2025 | 179 | 6.8% | 76.91% | 23.63 pp | $483M | 23% |
| Q4 2024 | 192 |
CSTL — Frequently Asked Questions
Quick answers to the most common questions about buying CSTL stock.
What percentage of CSTL is owned by institutions?
Based on Q1 2026 13F filings, institutional ownership of Castle Biosciences, Inc. stands at 104.0%, held across 183 reporting institutions.
Who is the largest institutional holder of CSTL?
BlackRock, Inc. is the largest reported institutional holder of CSTL, with approximately 2,982,946 shares worth $0.07B as of Q1 2026.
Is CSTL a hedge fund favorite?
Yes — 2 widely-followed marquee investors appear among the top 25 institutional holders of CSTL, including RENAISSANCE TECHNOLOGIES LLC, MILLENNIUM MANAGEMENT LLC.
What is CSTL's Smart Money Score?
Our composite Smart Money Score for CSTL is 39 out of 100 (Bearish). It combines net institutional buying activity, ownership shift, marquee investor presence, and holder-count growth.