Largest, Independent, Prospective Study Demonstrates Utility of DecisionDx®-Melanoma for Prediction of Outcomes in Patients With Cutaneous Melanoma Referred for Sentinel Node Biopsy

Castle Biosciences, Inc. (Nasdaq: CSTL), a skin cancer diagnostics company providing personalized genomic information to improve cancer treatment decisions, today announced data from an independent, prospective study published in the American Journal of Surgery demonstrating DecisionDx®-Melanoma’s utility for prediction of outcomes in patients with cutaneous melanoma. DecisionDx-Melanoma is Castle’s gene expression profile test that uses an individual patient’s tumor biology to predict risk of cutaneous melanoma metastasis or recurrence, as well as sentinel lymph node positivity, independent of traditional staging factors.

The publication, titled “Utility of a 31-gene expression profile for predicting outcomes in patients with primary cutaneous melanoma referred for sentinel node biopsy,” describes a study comparing tumor features, sentinel node biopsy (SLNB) results, and patient outcomes from a prospective database of 383 patients with cutaneous melanoma who both underwent SLNB and had their primary tumor assayed with DecisionDx-Melanoma. Groups were compared by univariate and multivariate analyses, and relapse-free and distant metastasis-free survival (RFS, DMFS) were estimated by Kaplan-Meier method.

The study’s results demonstrated that a Class 2 (high-risk) DecisionDx-Melanoma result was significantly associated with higher rates of SLNB positivity compared to Class 1 (low risk). With respect to risk prognoses, patients who received a Class 2B DecisionDx-Melanoma result and were SLNB-positive experienced the highest recurrence rates (38%), compared to only a 2% recurrence rate for patients who were Class 1A and SLNB-negative. DecisionDx-Melanoma Class 2 results were significantly associated with poorer RFS and DMFS rates compared to Class 1 results, both in the entire cohort of 383 cases and in patients staged as “low risk” (IA-IIA) according to American Joint Committee on Cancer (AJCC) staging criteria.

“We sought to study the utility of this 31 gene expression profile (31-GEP) test in the largest, independent, prospective study to date,” said corresponding author John T. Vetto, M.D., FACS, Professor of Surgery, Division of Surgical Oncology, Oregon Health & Science University, Portland. “Current staging parameters in melanoma are invaluable but also imperfect. We were encouraged to find that, like AJCC stage, the 31-GEP results were independently associated with patient outcomes, including recurrence and distant metastasis, and that the 31-GEP results added prognostic information when incorporated with existing features to evaluate patient risk.”

About DecisionDx-Melanoma

DecisionDx®-Melanoma is a gene expression profile test that uses an individual patient’s tumor biology to predict individual risk of cutaneous melanoma metastasis or recurrence, as well as sentinel lymph node positivity, independent of traditional staging factors, and has been studied in more than 5,700 patient samples. Using tissue from the primary melanoma, the test measures the expression of 31 genes. The test has been validated in four archival risk of recurrence studies of 901 patients and six prospective risk of recurrence studies including more than 1,600 patients. To predict likelihood of sentinel lymph node positivity, the Company utilizes its proprietary algorithm, i31-GEP, to produce an integrated test result. i31-GEP is an artificial intelligence-based neural network algorithm (independently validated in a cohort of 1,674 prospective, consecutively tested patients with T1-T4 cutaneous melanoma) that integrates the DecisionDx-Melanoma test result with the patient’s traditional clinicopathologic features. Impact on patient management plans for one of every two patients tested has been demonstrated in four multicenter and single-center studies including more than 560 patients. The consistent performance and accuracy demonstrated in these studies provides confidence in disease management plans that incorporate DecisionDx-Melanoma test results. Through December 31, 2020, DecisionDx-Melanoma has been ordered more than 68,920 times for use in patients with cutaneous melanoma.

More information about the test and disease can be found at www.CastleTestInfo.com.

About Castle Biosciences

Castle Biosciences (Nasdaq: CSTL) is a commercial-stage dermatologic cancer company focused on providing physicians and their patients with personalized, clinically actionable genomic information to make more accurate treatment decisions. The Company currently offers tests for patients with cutaneous melanoma (DecisionDx®-Melanoma, DecisionDx®-CMSeq), cutaneous squamous cell carcinoma (DecisionDx®-SCC), suspicious pigmented lesions (DecisionDx® DiffDx™-Melanoma) and uveal melanoma (DecisionDx®-UM, DecisionDx®-PRAME and DecisionDx®-UMSeq). For more information about Castle’s gene expression profile tests, visit www.CastleTestInfo.com. Castle also has active research and development programs for tests in other dermatologic diseases with high clinical need. Castle Biosciences is based in Friendswood, Texas (Houston), and has laboratory operations in Phoenix, Arizona. For more information, visit www.CastleBiosciences.com.

DecisionDx-Melanoma, DecisionDx-CMSeq, DecisionDx-SCC, DecisionDx DiffDx-Melanoma, DecisionDx-UM, DecisionDx-PRAME and DecisionDx-UMSeq are trademarks of Castle Biosciences, Inc.

Forward-Looking Statements

The information in this press release contains forward-looking statements and information 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 DecisionDx-Melanoma’s ability to accurately predict individual risk of cutaneous melanoma metastasis or recurrence, improve prognostic accuracy over sentinel lymph node biopsy results and add prognostic information. The words “anticipates,” “believes,” “estimates,” “expects,” “intends,” “may,” “plans,” “projects,” “will,” “would” 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, the effects of the COVID-19 pandemic on our business, subsequent study results and findings that contradict earlier study results and findings, DecisionDx-Melanoma’s ability to provide the aforementioned benefits to patients and the risks set forth in our Annual Report on Form 10-K for the year ended December 31, 2020, 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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