Castle Biosciences (CSTL) Q4 2025: TissueCypher Volume Soars 86%, Reinforcing GI Franchise Trajectory

February 26, 2026 | By EarningsIQ Research

TissueCypher, Castle Biosciences’ GI risk stratification test, delivered 86% volume growth in 2025, signaling accelerating adoption and validation of the company’s multi-year pipeline strategy. Dermatology and GI franchises both contributed to robust test growth, while gross margin compression and rising expenses highlight the cost of pipeline expansion and commercial scaling. Management’s 2026 guide and commentary point to a continued focus on core test adoption, measured pipeline rollout, and disciplined capital allocation as the company targets sustainable long-term growth.

Summary

• GI Penetration Accelerates: TissueCypher adoption surged, supported by clinical guideline recognition and expanding clinician base.
• Pipeline Expansion Drives Costs: Operating expenses rose as Castle invested in new tests, sales force, and R&D initiatives.
• 2026 Trajectory Anchored in Core Tests: Leadership signals continued focus on core dermatology and GI franchises for near-term growth.

Performance Analysis

Castle Biosciences’ 2025 performance was anchored by double-digit test volume growth in both its dermatology and gastroenterology franchises, with TissueCypher, a molecular risk stratification test for Barrett’s esophagus, standing out as the primary growth engine. TissueCypher test volumes rose 86% year-over-year, reaching 39,014 reports, and DecisionDx Melanoma volumes grew 9%, with the test surpassing 230,000 orders since launch. The core business, excluding discontinued and non-core revenue streams, would have grown approximately 34% for the year, reflecting robust underlying demand.

Gross margin for the year compressed to 69.2% from 78.5%, pressured by a $20.1 million one-time amortization expense and the loss of revenue from DecisionDx SCC. Adjusted gross margin also declined, reflecting a mix shift and higher costs associated with commercial expansion and pipeline investment. Operating expenses increased across sales, marketing, and G&A, driven by headcount, compensation, and commercial initiatives. Despite these cost pressures, Castle generated $64.3 million in operating cash flow and ended the year with nearly $300 million in cash and equivalents, supporting continued investment in growth.

• GI Franchise Momentum: TissueCypher’s 86% volume growth and 2,082 new ordering clinicians underscore expanding market penetration and guideline-driven adoption.
• Dermatology Resilience: DecisionDx Melanoma maintained high single-digit volume growth, with clinician adoption and peer-reviewed evidence supporting durable uptake.
• Margin Compression: Gross and adjusted EBITDA margins declined year-over-year, reflecting both one-time charges and structural cost increases tied to pipeline and sales force expansion.

Castle’s 2025 results reflect a business scaling its core franchises while absorbing the costs of pipeline build-out and commercial reach, setting the stage for a multi-year growth trajectory but with near-term margin and profitability trade-offs.

Executive Commentary

Strategic Positioning

1. GI Franchise: TissueCypher as Growth Engine

TissueCypher, a molecular test for Barrett’s esophagus risk stratification, has rapidly become a focal point for Castle’s growth strategy. Clinical guideline inclusion from the American Gastroenterological Association and the test’s ability to identify high-risk patients have driven both new clinician adoption and increased ordering volume. Management emphasized that TissueCypher is still in the early stages of penetration, with only 11% patient and roughly 25-30% clinician penetration, suggesting a long runway for growth.

2. Dermatology Franchise: Sustained Adoption and Evidence Base

DecisionDx Melanoma remains a durable revenue driver, with 9% volume growth and continued first-time ordering from clinicians. The test is supported by 58 peer-reviewed publications and ongoing efforts to achieve FDA clearance, which management expects will support reimbursement under state biomarker laws. The company’s disciplined approach to clinician education and evidence generation has built a defensible position in the dermatology market.

3. Pipeline and Commercial Expansion

Castle’s pipeline strategy is multi-pronged, with near-term focus on core tests, mid-term on ADVANCE-AD-TX (atopic dermatitis treatment guidance), and long-term on new GI diagnostics and technology collaborations. Early uptake of ADVANCE-AD-TX in a limited-access launch has been strong, though material revenue is not expected until 2027 or later. The company is also investing in new sample collection devices and EIS technology, with first patient enrollment for new studies targeted for 2026.

4. Capital Allocation and M&A

Management reiterated a disciplined M&A approach, targeting assets near commercialization or reimbursement that can be leveraged by the existing sales force. The balance sheet remains strong, enabling continued investment in both organic and inorganic growth opportunities.

Key Considerations

Castle’s 2025 results and 2026 outlook reflect a business at an inflection point, balancing aggressive franchise expansion with the realities of cost escalation and margin compression. Investors should weigh the following:

Key Considerations:

• Clinical Guideline Endorsement: TissueCypher’s inclusion in AGA guidelines is catalyzing adoption and could accelerate payer coverage and institutional uptake.
• Sales Force Scaling: Both GI and dermatology franchises are expanding sales teams, with management targeting sub-100 rep models for each specialty to maintain efficiency.
• Pipeline Revenue Timing: ADVANCE-AD-TX is seeing early demand, but material revenue contribution is not expected until 2027, highlighting a lag between clinical launch and financial impact.
• Margin Pressures: Structural cost increases from commercial and R&D investments are weighing on margins, with management signaling only moderate expense growth in 2026.
• Reimbursement and Regulatory Leverage: FDA submission for DecisionDx Melanoma aims to unlock broader reimbursement under state biomarker laws, potentially reducing nonpayment risk.

Risks

Castle faces several execution and market risks, including the potential for further gross margin compression if commercial scaling outpaces revenue growth, reimbursement headwinds for new and existing tests, and slower-than-expected adoption among late-adopter clinicians. Regulatory timelines for FDA submissions and new product launches remain uncertain, and competitive innovation in molecular diagnostics could erode share or pricing power.

Forward Outlook

For Q1 2026, Castle expects:

• Seasonally flat sequential test volumes for DecisionDx Melanoma, with a step up expected from Q1 to Q2.
• Continued strong volume growth for TissueCypher, though percentage growth rates may moderate as penetration rises.

For full-year 2026, management guided:

• Total revenue of $340 to $350 million, with growth driven by core dermatology and GI tests.
• Operating expense increases to be moderate, focused on core franchises and pipeline advancement.

Management highlighted:

• Immaterial revenue expected from ADVANCE-AD-TX in 2026, with material contributions in 2027-2028.
• Ongoing clinical evidence generation and strategic account focus in both GI and dermatology segments.

Takeaways

Castle’s 2025 performance validates its GI and dermatology franchise strategies, but margin compression and cost escalation reflect the realities of scaling a multi-product diagnostics platform.

• GI Franchise as Growth Anchor: TissueCypher’s rapid adoption and guideline recognition position Castle for continued GI revenue expansion, with significant white space remaining.
• Pipeline Investment Trade-Offs: The cost of commercial and R&D expansion is pressuring near-term profitability, but management is betting on long-term value creation from new tests and expanded indications.
• Watch for Reimbursement and Guideline Shifts: FDA clearance, payer policy changes, and further clinical endorsements will be key catalysts for both volume and margin inflection in coming years.

Conclusion

Castle Biosciences exits 2025 with strong test volume momentum in both GI and dermatology, a robust pipeline, and a well-capitalized balance sheet. The company’s disciplined approach to commercial expansion and innovation positions it for long-term growth, but investors should monitor margin trends and execution on reimbursement milestones as key determinants of value realization.

Industry Read-Through

Castle’s TissueCypher adoption surge and clinical guideline endorsement signal that molecular diagnostics with proven clinical utility can rapidly gain traction in specialty care, especially when supported by robust evidence and targeted sales execution. The margin compression and cost structure challenges highlight the capital intensity required to scale multi-indication platforms, a dynamic relevant for peers in oncology, GI, and dermatology diagnostics. FDA clearance as a lever for reimbursement under state biomarker laws is an emerging theme that could influence product strategies and payer negotiations across the diagnostics sector. Investors should watch for further guideline updates and payer policy shifts as leading indicators of adoption and market expansion for molecular tests.

CSTL Healthcare Diagnostics Molecular Testing Gastroenterology Dermatology Pipeline Reimbursement