Data Demonstrating DecisionDx®-Melanoma Was a Significant, Independent Predictor of Metastatic Recurrence in Stage I-III Cutaneous Melanoma Published in Future Oncology

Data demonstrated that patients with a DecisionDx-Melanoma Class 1A (low risk) test result had a five-year recurrence-free survival rate and distant metastasis-free survival rate of 95.8% and 99.2%, respectively

Castle Biosciences, Inc. (Nasdaq: CSTL), a company applying innovative diagnostics to transform disease management and improve patient outcomes, today announced the publication of a study of patients with stage I-III cutaneous melanoma. Data demonstrated that DecisionDx®-Melanoma is a significant independent predictor of metastatic recurrence.

DecisionDx-Melanoma is Castle’s gene expression profile (GEP) test that uses an individual patient’s tumor biology to predict the risk of cutaneous melanoma metastasis or recurrence, as well as the risk of sentinel lymph node (SLN) positivity, independent of traditional staging factors. The study, titled “The 31-gene expression profile stratifies recurrence and metastasis risk in patients with cutaneous melanoma,” analyzed 438 patients who were tested with DecisionDx-Melanoma as part of their clinical care. The study can be accessed here.

“This study reinforced one of the primary reasons why I order DecisionDx-Melanoma for my patients as soon as they receive a melanoma diagnosis,” said first author Abel Jarell, M.D., dermatologist and dermatopathologist at Northeast Dermatology Associates, Portsmouth, N.H. “It’s designed to provide personalized, prognostic information that I use to determine the likelihood that the cancer will spread, which helps inform decisions for treatment to ensure the best possible outcome for each patient’s disease.”

Study background and highlights:

• The study’s primary purpose was to show risk stratification by DecisionDx-Melanoma in patients with stage I–III cutaneous melanoma. A secondary end point was to demonstrate the added prognostic value of DecisionDx-Melanoma when combined with complete American Joint Committee on Cancer (AJCC) staging (including SLN status) or with SLN status alone, for recurrence detection.
• 438 patients with stage I–III melanoma consecutively tested with DecisionDx-Melanoma were analyzed and stratified as low risk (Class 1A), intermediate risk (Class 1B/2A) or high risk (Class 2B) of recurrence or metastasis.
• DecisionDx-Melanoma significantly stratified five-year melanoma survival prognoses for patients, including recurrence-free survival (RFS) (p<0.001), distant metastasis-free survival (DMFS) (p<0.001) and melanoma-specific survival (MSS) (p<0.001).
• Patients with a DecisionDx-Melanoma low-risk result (Class 1A) had higher five-year survival outcomes and were less likely to experience a recurrence than patients with a high-risk result (Class 2B).
• Multivariable analysis showed that DecisionDx-Melanoma is a significant, independent predictor of metastatic recurrence (hazard ratio=5.38, p=0.014).
• DecisionDx-Melanoma increased prognostic survival accuracy over sentinel lymph node status alone.
• Consistent with previous validation and performance studies, the study demonstrated that DecisionDx-Melanoma added independent prognostic value to current staging guidelines for cutaneous melanoma to identify patients with a high and low recurrence or metastasis risk to improve patient management.

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. 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. To predict risk of recurrence and likelihood of sentinel lymph node positivity, the Company utilizes its proprietary algorithms, i31-ROR and i31-SLNB, to produce an Integrated Test Result. Through Sept. 30, 2021, DecisionDx-Melanoma has been ordered 84,195 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 diagnostics 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 (myPath® Melanoma, 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, including its test in development to predict systemic therapy response in patients with moderate to severe psoriasis, atopic dermatitis and related conditions. Castle Biosciences is based in Friendswood, Texas (Houston), and has laboratory operations in Phoenix.

For more information, visit www.CastleBiosciences.com.

DecisionDx-Melanoma, DecisionDx-CMSeq, DecisionDx-SCC, myPath Melanoma, 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 predict the risk of cutaneous melanoma metastasis or recurrence, as well as the risk of SLN positivity, independent of traditional staging factors, be a significant independent predictor of metastatic recurrence, provide personalized, prognostic information that helps determine the likelihood that the cancer will spread, and inform decisions for treatment to ensure the best possible outcome for each patient’s disease. 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 and our efforts to address its impact 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 Quarterly Report on Form 10-Q for the quarter ended Sept. 30, 2021, 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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