Castle Biosciences (CSTL) Q1 2026 earnings review
Core Volumes Surge, But Legacy Headwinds Drag Down Revenue and Profitability
Castle Biosciences delivered a mixed Q1 2026. On the surface, the core business is thriving: TissueCypher and DecisionDx-Melanoma volumes jumped 58% and 16% YoY, respectively, prompting management to raise FY26 revenue guidance to $345-$355M. However, the financial reality of transitioning the business model is stark. Total revenue dropped 5% YoY to $83.7M, dragged down by the loss of DecisionDx-SCC Medicare coverage and the discontinuation of IDgenetix. More concerning is the reversing profitability: Adjusted EBITDA plunged into negative territory (-$5.1M) for the first time in over a year, and adjusted gross margins are steadily decelerating due to an unfavorable product mix shift. The company is successfully pivoting its volume base, but the new revenue streams are currently less profitable than the legacy ones they are replacing.
🐂 Bull Case
Total test reports for core revenue drivers increased 36% YoY. TissueCypher is proving to be a massive growth engine, supported by a large, underpenetrated TAM and recent AGA clinical guidelines.
Despite the Q1 revenue decline, management raised the FY26 revenue outlook from $340-$350M to $345-$355M, signaling confidence that core volume momentum will outpace the legacy SCC revenue runoff in the back half of the year.
🐻 Bear Case
Adjusted Gross Margin fell to 75.6% (from 81.2% a year ago). The mix shift toward the lower-margin TissueCypher test is structurally diluting the company's previously stellar margin profile.
While YoY numbers look fantastic, sequential QoQ growth for both TissueCypher and DecisionDx-Melanoma was completely flat or slightly down from Q4 2025 to Q1 2026.
⚖️ Verdict: ⚪
Neutral. Castle is executing well operationally by driving adoption of its core tests. However, the financial friction of replacing high-margin, reimbursed legacy tests (SCC) with lower-margin, scaling tests (TissueCypher) is taking a severe toll on the bottom line. Investors must wait for volume leverage to eventually restore EBITDA profitability.
Key Themes
TissueCypher is the Primary Growth Engine
TissueCypher test volumes surged 58% YoY to 11,745, cementing its status as Castle's most critical growth driver. This growth is driving a rapid structural shift in the company's revenue base, with non-dermatologic revenue hitting $42.6M in Q1, up 70% from $25.0M a year ago. The test benefits from a massive $1B TAM and inclusion in 2024 AGA guidelines.
Sequential Stagnation Contradicts Hyper-Growth Narrative
Management heavily promoted the 36% YoY growth in core volumes. However, plotting the data reveals a decelerating trend that has now flatlined. TissueCypher volumes actually dropped slightly sequentially (11,803 in 25Q4 to 11,745 in 26Q1), and DecisionDx-Melanoma was flat (10,022 to 10,021). If Q1 seasonality isn't solely to blame, the hyper-growth engine may be cooling faster than anticipated.
Structural Margin Compression
Adjusted Gross Margin is steadily decelerating, falling from 81.2% in 25Q1 to 75.6% in 26Q1. This is a direct consequence of product mix shift. The company lost Medicare coverage for DecisionDx-SCC (a high-margin test) and is replacing that revenue with TissueCypher, which carries a higher cost of goods sold. This structural shift means the company needs significantly more volume to generate the same gross profit dollars.
Robust Clinical Data Moat for Melanoma
DecisionDx-Melanoma volumes grew 16% YoY. Castle continues to build a massive clinical data moat, presenting new data showing the test's i31-SLNB algorithm identifies patients with a less than 5% predicted risk of sentinel lymph node positivity, resulting in an actual positivity rate of just 2.6%. This perfectly aligns with NCCN guideline thresholds to forgo biopsies, serving as a powerful tool for physician adoption despite ongoing friction with NCCN committees.
Industry/Macro: Navigating Reimbursement Hostility
Castle's entire business model is currently defined by its ability to navigate a hostile reimbursement landscape. The Q1 revenue decline is directly tied to Novitas pulling Medicare coverage for DecisionDx-SCC. The company's future hinges on either winning back coverage through reconsideration requests or rapidly scaling newer, fully reimbursed tests to outgrow the legacy losses.
Other KPIs
Reversing. Profitability collapsed compared to the $13.0M generated in the prior-year period and $11.5M in 25Q4. This was driven by lower total revenues, lower gross margins, and higher operating expenses required to support the expanding commercial infrastructure.
Decelerating significantly from -$6.0M in 25Q1. Management attributed this sharp burn to the seasonal payout of employee annual cash bonuses and certain non-recurring healthcare benefit payments totaling $28.8M. However, it underscores the increased cash intensity of the current operations.
Stable. Despite the Q1 cash burn, Castle maintains a fortress balance sheet. This provides ample runway to weather the SCC reimbursement headwind and fund the commercial rollout of AdvanceAD-Tx and pipeline GI initiatives without needing near-term dilution.
Guidance
Accelerating vs current quarter trends. Management raised the bottom and top ends of the range by $5M. The midpoint ($350M) implies roughly 2% YoY growth compared to the $344.2M generated in FY25. Achieving this will require sequential acceleration in core test volumes throughout the year to offset the heavy Q1 legacy revenue comps.
Key Questions
Sequential Stagnation in Core Volumes
TissueCypher and DecisionDx-Melanoma volumes were virtually flat from Q4 to Q1. How much of this is driven by expected Q1 seasonality versus sales force capacity constraints or market saturation in early-adopter cohorts?
Margin Floor
Adjusted Gross Margin has compressed over 500 basis points in the last year. Where does management see the floor for gross margins as TissueCypher continues to outgrow the legacy dermatology business?
Path to EBITDA Profitability
With Adjusted EBITDA turning negative in Q1 and operating expenses remaining elevated, what is the timeline and volume threshold required to return to consistent, positive Adjusted EBITDA?
AdvanceAD-Tx Revenue Contribution
AdvanceAD-Tx was launched in late 2025 in a limited capacity. When does management expect this test to begin providing a material contribution to top-line revenue, and what are the primary reimbursement milestones needed to get there?