Castle Biosciences Presents New Data Demonstrating the Ability of DecisionDx®-SCC to Identify Tumors Likely to Metastasize in Patients with Cutaneous Squamous Cell Carcinoma Deemed Low Risk by Traditional Staging

Data shared during the 2023 Fall Clinical Dermatology Conference for PAs & NPs^®

Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced new data demonstrating the ability of the DecisionDx^®-SCC test to identify cutaneous squamous cell carcinoma (cSCC) tumors at a biologically high risk of metastasis in a subset of patients considered to be at a low risk of metastasis by traditional staging (i.e., patients with T1 tumors under the American Joint Committee on Cancer Eighth Edition (AJCC8) and Brigham and Women’s Hospital (BWH) staging systems). The data was shared in a poster, titled “The 40-gene expression profile (40-GEP) test allows for an improved prognostication of the likelihood of metastasis in patients with T1 cutaneous squamous cell carcinoma (cSCC) with high-risk factors,” during the recent 2023 Fall Clinical Dermatology Conference for PAs & NPs^®.

“Traditional staging, which includes solely tumor characteristics, only tells part of the story and leaves out a very critical piece of the plot, the biology of an individual patient’s tumor, which can provide greater insight into each patient’s unique metastatic propensity,” said Ally-Khan Somani, M.D., Ph.D., board-certified dermatologist, Mohs micrographic surgeon and director of Dermatologic Surgery & Cutaneous Oncology Division at the Indiana University School of Medicine in Indianapolis. “By estimating a cSCC patient’s personal risk of metastasis, the DecisionDx-SCC test has proven to elevate the narrative, which can lead to more informed, pertinent risk-aligned treatment decisions that can help improve outcomes.”

In the study, the DecisionDx-SCC test was able to significantly stratify three-year metastasis free survival rates within the AJCC8 and BWH T1 populations of the cSCC cohort. Approximately 70% of the AJCC8- and BWH-staged T1 tumors that metastasized were identified as being biologically high-risk by the DecisionDx-SCC test. This data supports the ability of the test to improve risk assessments based on staging alone, enabling clinicians and patients to make more risk-appropriate surveillance and treatment decisions.

Castle’s poster will be published in SKIN, The Journal of Cutaneous Medicine^® (www.jofskin.org), and may also be viewed here.

About DecisionDx^®-SCC

DecisionDx-SCC is a 40-gene expression profile test that uses an individual patient’s tumor biology to predict individual risk of cutaneous squamous cell carcinoma metastasis for patients with one or more risk factors. The test result, in which patients are stratified into a Class 1 (low), Class 2A (moderate) or Class 2B (high) risk category, predicts individual metastatic risk to inform risk-appropriate management.

Peer-reviewed publications have demonstrated that DecisionDx-SCC is an independent predictor of metastatic risk and that integrating DecisionDx-SCC with current prognostic methods can add positive predictive value to clinician decisions regarding staging and management. More information about the disease and test can be found at www.CastleTestInfo.com.

About Castle Biosciences

Castle Biosciences (Nasdaq: CSTL) is a leading diagnostics company improving health through innovative tests that guide patient care. The Company aims to transform disease management by keeping people first: patients, clinicians, employees and investors.

Castle’s current portfolio consists of tests for skin cancers, uveal melanoma, Barrett’s esophagus and mental health conditions. Additionally, the Company has active research and development programs for tests in other diseases with high clinical need, including its test in development to predict systemic therapy response in patients with moderate-to-severe psoriasis, atopic dermatitis and related conditions. To learn more, please visit www.CastleBiosciences.com and connect with us on LinkedIn, Facebook, Twitter and Instagram.

DecisionDx-Melanoma, DecisionDx-CMSeq, DecisionDx-SCC, MyPath Melanoma, DecisionDx-UM, DecisionDx-PRAME, DecisionDx-UMSeq, TissueCypher and IDgenetix 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 potential of DecisionDx-SCC to (i) provide greater insight into each patient’s unique metastatic propensity and (ii) lead to more informed, pertinent risk-aligned treatment decisions that can help improve outcomes. The words “can,” “potential” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. We may not actually achieve the plans, 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 our 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 this study, including with respect to the discussion of DecisionDx-SCC in this press release; actual application of our tests may not provide the aforementioned benefits to patients; and the risks set forth under the heading “Risk Factors” in our Quarterly Report on Form 10-Q for the three months ended March 31, 2023, 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.

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