In the study, patients with DecisionDx-SCC Class 2B test results, predicted to have the highest risk of metastasis by the test, who were treated with adjuvant radiation therapy (ART) had 50% higher metastasis-free survival (MFS) rates, on average, and slowed disease progression compared to Class 2B patients who did not receive ART

Patients with Class 1 test results, predicted to have a lower risk of metastasis, did not see an improvement in survival after receiving ART, which together indicates these patients may be able to avoid the treatment

Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced the publication of a study in the International Journal of Radiation Oncology • Biology • Physics (Red Journal) demonstrating the ability of the DecisionDx-SCC test to identify high-risk cutaneous squamous cell carcinoma (SCC) patients at the highest risk of metastasis who will benefit the most from ART to reduce metastatic disease progression, as well as high-risk patients who the test identified as having a lower risk of metastasis who may consider deferring treatment. These results demonstrate the impact of the test in guiding decision-making for recommending ART.

“Radiation may be considered for patients with more aggressive SCC tumors to reduce the risk of the cancer returning once the tumor has been removed through surgery,” said Sarah T. Arron, M.D. Ph.D., lead author and board-certified dermatologist and Mohs surgeon at Peninsula Dermatology in Burlingame, California. “When relying on current risk assessment and staging systems alone, it can be very challenging to determine for which patients with high-risk SCC the benefits of radiation therapy outweigh the significant side effects and associated impacts on the patient’s quality of life.

“The study found that DecisionDx-SCC test results can assist clinicians in making these difficult decisions by identifying which patients are most likely to benefit from the treatment.”

Key findings of the study (n=920 patients) include:

• The DecisionDx-SCC test identified patients projected to receive the greatest benefit from ART to reduce metastatic disease progression. Patients with a Class 2B (highest metastatic risk) test result who were treated with ART had 50% higher MFS rates, on average, than Class 2B patients who did not receive ART at five years post-diagnosis.
• A DecisionDx-SCC Class 2B result was the only independent risk factor that successfully identified patients who would most benefit from ART. Risk factors in the analysis included differentiation status, invasion into fat, perineural invasion and others, including National Comprehensive Cancer Network (NCCN) risk category and Brigham and Women's Hospital and American Joint Committee on Cancer Eighth Edition T-stages.
• Class 2B patients who received ART showed a significant deceleration in disease progression compared to Class 2B patients who did not receive ART. For patients with a DecisionDx-SCC Class 2B test result who were not treated with ART, there was a peak rate of metastasis around two years; Class 2B, ART-treated patients had nearly five times longer projected time to metastasis.
• DecisionDx-SCC identified patients who were less likely to show a significant benefit from ART in controlling disease progression. Patients with high-risk clinicopathologic features but who received a DecisionDx-SCC Class 1 (lower metastatic risk) test result did not show a significant benefit from ART. Given the low risk of metastasis for Class 1 patients, in addition to the lower likelihood of ART benefit, Class 1 patients may consider deferring treatment.

About DecisionDx-SCC

DecisionDx-SCC is a 40-gene expression profile test that uses an individual patient’s tumor biology to stratify risk of metastasis in patients with cutaneous squamous cell carcinoma who have one or more NCCN high-risk factors. The test result, in which patients are stratified into a Class 1 (lower), Class 2A (higher) or Class 2B (highest) risk category, predicts individual metastatic risk to inform risk-appropriate management and guide decision-making regarding the use of adjuvant radiation therapy. Peer-reviewed publications have demonstrated that DecisionDx-SCC is an independent predictor of metastatic risk and that the test can significantly improve risk-stratification when used with traditional staging systems and clinicopathologic risk factors to guide risk-aligned management and treatment decisions. Learn more at www.CastleBiosciences.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, Barrett’s esophagus, mental health conditions and uveal melanoma. Additionally, the Company has active research and development programs for tests in other diseases with high clinical need, including its test in development to help guide systemic therapy selection for patients with moderate-to-severe atopic dermatitis, psoriasis and related conditions. To learn more, please visit www.CastleBiosciences.com and connect with us on LinkedIn, Facebook, X and Instagram.

DecisionDx-Melanoma, DecisionDx-CMSeq, DecisionDx-SCC, MyPath Melanoma, DiffDx-Melanoma, TissueCypher, IDgenetix, 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 continued ability of the DecisionDx-SCC test to identify patients with high-risk SCC who would most likely benefit from ART based on the biological risk of metastasis. The words “can,” “may” 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 shown 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 Annual Report on Form 10-K for the year ended December 31, 2023, our Quarterly Report on Form 10-Q for the quarter ended March 31, 2024 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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