Independent Data Presented at Society for Surgical Oncology Conference Demonstrated DecisionDx®-Melanoma Outperforms T-Stage at Identifying Patients with Low Risk of Sentinel Lymph Node Positivity

FRIENDSWOOD, Texas--(BUSINESS WIRE)-- Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced new data further demonstrating the performance of DecisionDx®-Melanoma and i31-SLNB to provide improved risk prediction of sentinel lymph node (SLN) positivity, compared to using T-stage factors alone, in patients with cutaneous melanoma. The data will be shared in a poster presentation at the Society of Surgical Oncology (SSO) 2022 International Conference on Surgical Cancer Care, being held in Dallas and virtually, March 9-12, 2022.

“While the sentinel lymph node biopsy (SLNB) surgical procedure is a common technique in determining possible tumor metastasis, our current criteria for biopsy may be overestimating a person’s risk of having a positive node. This means we may be doing more sentinel node biopsies than necessary; and while we certainly don’t want to miss any lymph node metastases, we also don’t want to do procedures unnecessarily,” said study author Joseph Bennett, M.D., Chief of Surgical Oncology and Director of the Melanoma and Sarcoma Multidisciplinary Clinic at ChristianaCare Helen F. Graham Cancer Center & Research Institute, Newark, Del. “The study data show that DecisionDx-Melanoma has the ability to more accurately stratify risk for melanoma patients, which can help guide risk-aligned discussions about which patients should be offered the SLNB procedure and which can forgo it, based on their personal, biologic risk of a positive SLN. We expect that by using DecisionDx-Melanoma and i31-SLNB in addition to standard criteria, we can avoid doing SLNB procedures in many low-risk patients without missing melanoma metastases.”

The poster, titled “Integrating the 31-gene expression profile test with clinical and pathologic features can provide personalized precision estimates for sentinel lymph node positivity,” evaluated the performance of DecisionDx-Melanoma’s proprietary i31-SLNB algorithm in predicting the risk of SLNB positivity in 156 melanoma patients with known SLN outcomes at the ChristianaCare Helen F. Graham Cancer Center & Research Institute.

In the study, the DecisionDx-Melanoma test outperformed T-stage in identifying patients with low-risk tumors who could forgo SLNB, with an Area Under the Curve (AUC) of 0.89 versus 0.78 for T-stage in patients with T1-T2 tumors, indicating that DecisionDx-Melanoma provides improved predictions compared to those of the T-stage system. Additionally, the test accurately identified all patients with T1-T2 tumors who had a low risk (<5%) of SLN positivity (all of whom had negative SLNB results) with 100% negative predictive value, 100% sensitivity and significantly improved specificity compared to T-stage (37.5% vs. 2.5% for T-stage). Using T-stage alone, only two patients (T1a with no other high-risk tumor features) were accurately identified as low risk (<5%) of SLN positivity.

“The results of the study demonstrate that DecisionDx-Melanoma, with its proprietary i31-SLNB algorithm, can allow for more precise and personalized management of melanoma patients and improve patient selection for the SLNB surgical procedure, thus potentially enabling a reduction in unnecessary healthcare costs,” said Derek Maetzold, president and chief executive officer of Castle Biosciences.

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 risk of sentinel lymph node positivity, independent of traditional staging factors, and has been studied in more than 6,000 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 Dec. 31, 2021, DecisionDx-Melanoma has been ordered 90,154 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 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 and Barrett’s esophagus. 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 DiffDx-Melanoma, DecisionDx-UM, DecisionDx-PRAME, DecisionDx-UMSeq and TissueCypher 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 more accurately stratify risk for melanoma patients and guide risk-aligned discussions with patients regarding the SLNB procedure; the overall ability of DecisionDx-Melanoma to allow for more precise and personalized management of melanoma patients and improve patient selection for the SLNB surgical procedure; and the potential for decreased healthcare costs resulting from DecisionDx-Melanoma test result. 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 may contradict earlier study results and findings, including with respect to the discussion of DecisionDx-Melanoma in this press release, actual application of our tests to patients may not provide the aforementioned benefits observed in the retrospective study, and the risks set forth under the heading “Risk Factors” in our Annual Report on Form 10-K for the twelve months ended Dec. 31, 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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