Castle Biosciences to Present New Data at 2024 ASCO® Annual Meeting Highlighting Use of DecisionDx®-Melanoma to Identify Early-Stage Melanoma Patients at High Risk of Metastasis to the Central Nervous System to Prompt Use of Imaging Surveillance

Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced that it will present new data related to its DecisionDx-Melanoma and DecisionDx-UM tests at the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting, being held May 31-June 4, 2024, in Chicago.

"Harnessing the biology of tumors through our DecisionDx family of gene expression profile tests can help guide decision-making about the most appropriate cancer treatment pathway for patients aligned to their risk of metastasis," said Derek Maetzold, president and chief executive officer of Castle Biosciences. "The findings we are presenting at ASCO demonstrate the clinically meaningful risk stratification provided by our tests and support their utility in helping inform risk-aligned treatment and care for patients diagnosed with cutaneous and uveal melanoma to improve cancer outcomes."

Castle's presentations at ASCO will take place during the Melanoma/Skin Cancers poster session on Saturday, June 1 from 1:30-4:30 p.m. Central time in Hall A.

DecisionDx-Melanoma

• Title: The 31-GEP identifies patients with localized cutaneous melanoma at the highest risk of metastasis to the central nervous system
• Abstract: 9530
• Poster Bd #: 314
• Key take-aways: Cutaneous melanoma (CM) metastasis to the central nervous system (CNS) has a poor prognosis; however, patients generally experience better outcomes if CNS metastases are detected and treated earlier when the patient is still asymptomatic. CNS imaging is not routinely recommended for patients with early-stage CM (American Joint Committee on Cancer 8th edition (AJCC8) stage I?II), yet approximately 14% of patients with stage II melanoma will develop CNS metastases. This study demonstrated that the DecisionDx-Melanoma test can identify patients with earlier-stage melanoma who have a higher risk of CNS metastasis within the first three years post-diagnosis. These higher-risk patients may benefit from more frequent imaging surveillance to identify CNS metastases earlier to improve patient survival. Patients with Class 2B (highest risk) DecisionDx-Melanoma test results had higher rates of CNS metastases and lower five-year recurrence free survival than patients with Class 1A (lowest risk) or Class 1B/2A (increased risk) test results (p<0.001). Further, the study showed that a Class 2B (high risk) DecisionDx-Melanoma test result was the only significant predictor of CNS metastasis in multivariable analyses that included clinicopathologic-based risk factors considered in AJCC8 staging (HR (95% CI) 9.21 (2.72-31.19); p<0.001).

DecisionDx-UM

• Title: The 15-gene expression profile test is independent from PRAME and 7-gene next-generation sequencing: Results from 3,267 clinically tested uveal melanomas
• Abstract: 9598
• Poster Bd #: 382
• Key take-aways: This study is the largest to date to describe the combined performance of Castle's comprehensive suite of UM tests, which includes the prognostic DecisionDx-UM test and two ancillary tests: Preferentially Expressed Antigen in Melanoma (PRAME) status (DecisionDx-PRAME) and DNA mutation status (DecisionDx-UMSeq). The study explored associations across test results and found that neither PRAME expression status nor the presence of mutations in putative prognostic genes (BAP1, SF3B1 and EIF1AX) to be adequate surrogates for the DecisionDx-UM Class result. Given the extensive data supporting DecisionDx-UM as the most accurate predictor of metastatic outcomes, including recently presented data from the largest prospective performance study of DecisionDx-UM to date, which included more than 1,500 patients from 26 centers, study authors recommend that PRAME and DNA mutation status be considered in the context of a DecisionDx-UM result to further refine metastatic risk and inform risk-aligned treatment plans.

The full abstracts outlined above can be found at the ASCO website here.

About DecisionDx-Melanoma

DecisionDx-Melanoma is a gene expression profile risk stratification test. It is designed to inform two clinical questions in the management of cutaneous melanoma: a patient's individual risk of sentinel lymph node (SLN) positivity and a patient's personal risk of melanoma recurrence and/or metastasis. By integrating tumor biology with clinical and pathologic factors using a validated proprietary algorithm, DecisionDx-Melanoma is designed to provide a comprehensive and clinically actionable result to guide risk-aligned patient care. DecisionDx-Melanoma has been shown to be associated with improved patient survival and has been studied in more than 10,000 patient samples. DecisionDx-Melanoma's clinical value is supported by 50 peer-reviewed and published studies, providing confidence in disease management plans that incorporate the test's results. Through March 31, 2024, DecisionDx-Melanoma has been ordered more than 164,000 times for patients diagnosed with cutaneous melanoma. More information about the test and disease can be found here.

About DecisionDx-UM

DecisionDx-UM is Castle Biosciences' 15-gene expression profile (GEP) test that uses an individual patient's tumor biology to predict individual risk of metastasis in patients with uveal melanoma (UM). DecisionDx-UM is the standard of care in the management of newly diagnosed UM in the majority of ocular oncology practices in the United States. Since 2009, the American Joint Committee on Cancer (AJCC; v7 and v8) Staging Manual for UM has specifically identified the GEP test as a prognostic factor that is recommended for collection as a part of clinical care. Further, the National Comprehensive Cancer Network (NCCN) guidelines for UM include the DecisionDx-UM test result as a prognostic method for determining risk of metastasis and recommend differential surveillance regimens based on a Class 1A, 1B and 2 result. DecisionDx-UM is currently the only prognostic test for UM that has been validated in prospective, multi-center studies, and it has been shown to be a superior predictor of metastasis compared to other prognostic factors, such as chromosome 3 status, mutational status, AJCC stage and cell type. It is estimated that nearly 8 in 10 patients diagnosed with UM in the United States receive the DecisionDx-UM test as part of their diagnostic workup. More information about the test and disease can be found here.

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: (i) the ability of the DecisionDx-Melanoma test to identify patients with earlier-stage melanoma who have a higher risk of CNS metastasis within the first three years post-diagnosis and (ii) the ability of DecisionDx-UM test to accurately predict metastatic outcomes. The words "believe," "can," "could," "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 these studies, including with respect to the discussion of our tests 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.