Castle Biosciences to Present New Data Demonstrating DecisionDx®-Melanoma's Ability to Identify Patients with Greater Risk of Recurrence and Poor Outcomes Within Early-Stage Melanoma at EADO and ACMS

Multi-center clinical and population-based data show that DecisionDx-Melanoma identifies biologically high-risk patients—including those with thin and early-stage disease—and provides recurrence risk insights to guide more precise, risk-aligned clinical management

FRIENDSWOOD, Texas, April 21, 2026 /PRNewswire/ -- Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced it will present new data on its DecisionDx-Melanoma test addressing a critical clinical challenge in melanoma care: identifying which patients with early-stage disease are at risk for poor outcomes and may benefit from intensified management. The data will be presented at the 22^nd European Congress of Dermato-Oncology (EADO) Congress and the American College of Mohs Surgery (ACMS) 58^th Annual Meeting. 

The data to be presented at both meetings further demonstrate that DecisionDx-Melanoma provides clinically actionable, personalized information that refines risk assessment across patients with cutaneous melanoma (CM). Notably, the data show the test can identify patients with thin tumors and early-stage disease whose outcomes may be more consistent with higher-risk melanoma and whose recurrence and survival risk may be underestimated by American Joint Committee on Cancer (AJCC) staging alone, enabling more precise, risk-aligned clinical management. 

"Some of the most important melanoma treatment decisions are made early, when risk is often difficult to assess, underscoring the need to confidently escalate care or avoid unnecessary interventions," said Rebecca Critchley-Thorne, Ph.D., vice president, research and development, at Castle Biosciences. "These studies further demonstrate the ability of DecisionDx-Melanoma to identify patients who may be at greater risk than expected based on staging alone, while also providing individualized recurrence risk information to support more informed management decisions. This information complements traditional clinicopathologic factors and helps guide decisions consistent with National Comprehensive Cancer Network^® guideline risk thresholds, including those related to sentinel lymph node biopsy and surveillance intensity." 

Details of the Company's poster at EADO, taking place in Prague, Czech Republic, from April 23-25, 2026, are as follows: 

• Poster title: The 31-GEP provides personalized prognostic information beyond AJCC staging in patients with cutaneous melanoma 
• Poster number: A-275 

At EADO, data are being presented from a large, multi‑center cohort of 1,817 patients with stage I–III CM that show DecisionDx‑Melanoma provides independent, personalized prognostic information beyond AJCC staging. In the study, the test significantly improved 5‑year recurrence risk prediction when combined with staging and identified biologically high‑risk patients within early‑stage disease (stage I–IIA). These patients had recurrence rates comparable to those with higher‑stage melanoma (stage IIB-IIIA), highlighting clinically meaningful differences in risk within early-stage disease that are not fully captured by traditional staging. These findings underscore the value of the DecisionDx-Melanoma test in supporting more precise, risk-aligned management decisions, including identifying patients who may benefit from closer surveillance or referral to multidisciplinary care teams.

Details of the Company's poster at ACMS, taking place in Austin, Texas, from April 30-May 3, 2026, are as follows: 

• ePoster title: The 31-gene expression profile test stratifies melanoma-specific survival among patients with AJCC T1a and T1b cutaneous melanoma: A 5-year outcome SEER population study 

The study to be shared at ACMS analyzes population-based Surveillance, Epidemiology and End Results (SEER) registry data showing that DecisionDx‑Melanoma can provide prognostic insight beyond AJCC staging in patients with thin T1a and T1b CM. The test identified molecularly high‑risk T1 patients with significantly lower 5‑year melanoma‑specific survival and, when combined with staging, identified more patients who died from melanoma than a stage III classification alone. These findings support the use of DecisionDx-Melanoma to inform more precise, risk-aligned management in a population often considered low risk, including identifying patients who may otherwise go unrecognized as high risk and who may benefit from closer surveillance or more proactive management. This poster is also part of Castle's ongoing collaboration leveraging data from the National Cancer Institute's SEER Program registries. 

About DecisionDx-Melanoma 
DecisionDx-Melanoma is a gene expression profile (GEP) test designed to analyze tumor biology to deliver a personalized risk assessment for patients with stage I–III cutaneous melanoma, enhancing risk stratification beyond American Joint Committee on Cancer (AJCC) staging alone. By combining molecular insights with select clinicopathologic features, the test provides two distinct outputs: a personalized risk of sentinel lymph node (SLN) positivity and a personalized risk of recurrence and/or metastasis. This clinically actionable information is designed to help guide risk-aligned patient management decisions, including SLN biopsy consideration, follow-up intensity, imaging and referrals. 

DecisionDx-Melanoma is supported by 58 peer-reviewed publications, including prospective studies and meta-analyses, and was developed in collaboration with more than 100 leading U.S. institutions. The test has been clinically validated in more than 10,000 patient samples, ordered more than 230,000 times since launch, and has been shown to be associated with improved patient survival. Learn more at castlebiosciences.com/tests/prognostic/decisiondx-melanoma/overview.

About Castle Biosciences 
Castle Biosciences (Nasdaq: CSTL) is a leading diagnostics company improving health through innovative tests that guide patient care. With a primary focus in dermatologic and gastroenterological disease, we develop personalized, clinically actionable solutions that help improve disease management and patient outcomes. 

We put people first—empowering patients and clinicians and informing care decisions through rigorous science and advanced molecular tests that support more confident treatment planning. To learn more, visit www.CastleBiosciences.com and connect with us on LinkedIn, Instagram, Facebook and X.

DecisionDx-Melanoma, DecisionDx-CMSeq, i31-SLNB, i31-ROR, DecisionDx-SCC, MyPath Melanoma, AdvanceAD-Tx, TissueCypher, DecisionDx-UM, DecisionDx-PRAME and DecisionDx-UMSeq are trademarks of Castle Biosciences, Inc. 

Forward-Looking Statements 
This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, which are subject to the "safe harbor" created by those sections. These forward-looking statements include, but are not limited to, statements concerning: the ability of DecisionDx-Melanoma to (i) help clinicians more confidently escalate care for higher-risk patients while avoiding unnecessary interventions in those at lower risk of poor outcomes; (ii) identify patients at higher or lower risk than predicted by AJCC staging alone, including high-risk T1 (thin) tumors with mortality risk approaching that of thicker melanomas; (iii) support more personalized management decisions by delivering a personalized risk assessment; (iv) significantly improve recurrence risk prediction when combined with AJCC staging, including the identification of biologically high-risk patients within early-stage disease; and (v) provide information consistent with NCCN guideline risk thresholds, including with respect to sentinel lymph node biopsy and surveillance intensity decisions. The words "designed," "may," "can," "provides," "helps guide," and similar expressions are intended to identify forward intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements that we make. These forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from those in the forward-looking statements, including, without limitation: subsequent study or trial results and findings may contradict earlier study or trial results and findings or may not support the results obtained in these studies, including with respect to the discussion of our tests in this press release; actual application of our tests may not provide the aforementioned benefits to certain patients; and the risks set forth under the heading "Risk Factors" in our Annual Report on Form 10-K for the year ended December 31, 2025, and our subsequent Quarterly Reports on Form 10-Q, each as filed or to be filed with the SEC, and in our other filings with the SEC. The forward-looking statements are applicable only as of the date on which they are made, and we do not assume any obligation to update any forward-looking statements, except as may be required by law.

SOURCE Castle Biosciences, Inc.