Castle Biosciences, Inc.
US ˙ NasdaqGM ˙ US14843C1053

SecurityCSTL / Castle Biosciences, Inc.
InstitutionParallel Advisors, LLC
Latest Disclosed Ownership13,986 shares
Latest Disclosed Value $ 544,055
Parallel Advisors, LLC ownership in CSTL / Castle Biosciences, Inc.

On February 11, 2026 - Parallel Advisors, LLC filed a 13F-HR form disclosing ownership of 13,986 shares of Castle Biosciences, Inc. (US:CSTL) valued at $544,055 USD as of December 31, 2025. The entity filed a previous 13F-HR on November 13, 2025 disclosing 17,786 shares of Castle Biosciences, Inc.. This represents a change in shares of -21.37% during the quarter. The current value of the position is $285,175 USD.

Parallel Advisors, LLC has a history of taking positions in derivatives of the underlying security (CSTL) in the form of stock options. The firm currently holds call options representing 0 of underlying shares valued at $0 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

CSTL / Castle Biosciences, Inc. Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-02-11 2025-12-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 13,986 -3,800 -21.37 544 34.65 0.0100
2025-11-13 2025-09-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 17,786 -10,107 -36.23 405 -29.00 0.0074
2025-07-08 2025-06-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 27,893 300 1.09 570 3.45 0.0114
2025-04-08 2025-03-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 27,593 -402 -1.44 551 -26.27 0.0124
2025-02-10 2024-12-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 27,995 3 0.01 746 -6.52 0.0168
2024-11-13 2024-09-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 27,992 1,524 5.76 798 38.54 0.0188
2024-08-08 2024-06-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 26,468 -200 -0.75 576 -2.37 0.0148
2024-05-06 2024-03-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 26,668 -300 -1.11 591 1.55 0.0160
2024-02-12 2023-12-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 26,968 0 0.00 582 27.69 0.0173
2024-05-20 2023-09-30 13F/A-1 CASTLE BIOSCIENCES INC COM Stock 14843C105 26,968 -87 -0.32 455 22.64 0.0152
2023-11-14 2023-09-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 26,968 -87 455 0.0152
2024-05-20 2023-06-30 13F/A-1 CASTLE BIOSCIENCES INC COM Stock 14843C105 27,055 4,986 22.59 371 -25.95 0.0120
2023-08-04 2023-06-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 27,055 4,986 371 0.0120
2024-05-20 2023-03-31 13F/A-1 CASTLE BIOSCIENCES INC COM Stock 14843C105 22,069 0 0.00 501 -3.47 0.0169
2023-04-25 2023-03-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 22,069 0 501 0.0169
2023-02-06 2022-12-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 22,069 -22 -0.10 520 -9.90 0.0225
2022-11-10 2022-09-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 22,091 0 0.00 576 18.76 0.0265
2022-08-01 2022-06-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 22,091 182 0.83 485 -49.69 0.0223
2022-04-28 2022-03-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 21,909 140 0.64 964 3.32 0.0383
2022-01-20 2021-12-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 21,769 0 0.00 933 -35.57 0.0346
2021-11-02 2021-09-30 13F/A-1 CASTLE BIOSCIENCES INC COM Stock 14843C105 21,769 -22 -0.10 1,448 -9.39 0.0584
2021-08-06 2021-06-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 21,791 1,791 8.96 1,598 16.73 0.0677
2021-04-23 2021-03-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 20,000 -5,000 -20.00 1,369 -18.46 0.0646
2021-02-02 2020-12-31 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 25,000 -14,420 -36.58 1,679 -17.21 0.0911
2020-10-27 2020-09-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 39,420 19,420 97.10 2,028 169.32 0.1255
2020-07-16 2020-06-30 13F CASTLE BIOSCIENCES INC COM Stock 14843C105 20,000 20,000 753 0.0491
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2022-01-19 2021-12-31 13F CASTLE BIOSCIENCES INC COM Stock Call 0 -100.00 0 -100.00 n/a n/a n/a
2021-10-22 2021-09-30 13F CASTLE BIOSCIENCES INC COM Stock Call 21,791 1,598 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.