New Data Highlights Clinical Utility and Performance of Castle Biosciences' Dermatologic Test Portfolio at the 2023 Fall Clinical Dermatology Conference®

Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced that it will share new data across its dermatologic portfolio of gene expression profile (GEP) tests at the 2023 Fall Clinical Dermatology Conference® (FC23), taking place Oct. 19-22, 2023, in Las Vegas.

"The breadth of data we are sharing at Fall Clinical reinforces our commitment to improving the care of patients with skin cancers and inflammatory skin conditions through innovative tests that can guide more informed disease management decisions," said Derek Maetzold, president and chief executive officer of Castle Biosciences.

Details regarding Castle's posters at FC23 are included below. Posters will be available for viewing for the duration of the conference.

• Using 31-gene expression profile testing to help guide adjuvant therapy and sentinel lymph node biopsy discussions with patients: A case series
  Lead Author: Peter Prieto, M.D., MPH, University of Rochester Medical Center

• Association of a 40-gene expression profile with risk of metastatic disease progression of cutaneous squamous cell carcinoma (cSCC) and benefit of adjuvant radiation therapy (ART)
  Lead Author: Sarah Arron, M.D., Ph.D., Peninsula Dermatology

• Incorporating the 40-gene expression profile (40-GEP) test within each clinicopathologic staging system improves metastatic risk-stratification in patients diagnosed with cutaneous squamous cell carcinoma (cSCC) and one or more high risk factors
  Lead Author: Ashley Wysong, M.D., M.S., University of Nebraska Medical Center

• Use of the 40-gene expression profile (40-GEP) test in Medicare-eligible patients diagnosed with cutaneous squamous cell carcinoma (cSCC) to guide adjuvant radiation therapy (ART) decisions leads to a significant reduction in healthcare costs
  Lead Authors: Anesh Prasai, Ph.D., Castle Biosciences, and Matthew S. Goldberg, M.D., Castle Biosciences and Icahn School of Medicine at Mount Sinai

• Performance of the 23-gene expression profile (23-GEP) test by histopathological evaluation in an independent, multi-center performance cohort of cutaneous melanocytic neoplasms
  Lead Author: Matthew S. Goldberg, M.D., Castle Biosciences and Icahn School of Medicine at Mount Sinai

• Gene expression differences identified in skin samples of early-stage mycosis fungoides, atopic dermatitis, and psoriasis
  Lead Author: Aaron S. Farberg, M.D., Baylor Scott & White Health System and Bare Dermatology
  Specific details regarding this poster will be shared following the FC23 conference.

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 more than 40 peer-reviewed and published studies, providing confidence in disease management plans that incorporate the test's results. Through June 30, 2023, DecisionDx-Melanoma has been ordered more than 137,200 times for patients diagnosed with cutaneous melanoma.

About DecisionDx®-SCC
DecisionDx-SCC is a 40-gene expression profile test that uses an individual patient's tumor biology to predict individual risk of cutaneous squamous cell carcinoma metastasis for patients with one or more risk factors. The test result, in which patients are stratified into a Class 1 (low), Class 2A (moderate) or Class 2B (high) risk category, predicts individual metastatic risk to inform risk-appropriate management. Peer-reviewed publications have demonstrated that DecisionDx-SCC is an independent predictor of metastatic risk and that integrating DecisionDx-SCC with current prognostic methods can add positive predictive value to clinician decisions regarding staging and management.

About MyPath® Melanoma
MyPath Melanoma is Castle's gene expression profile test designed to provide an accurate, objective result to aid dermatopathologists and dermatologists in characterizing difficult-to-diagnose melanocytic lesions. Of the approximately two million suspicious pigmented lesions biopsied annually in the U.S., Castle estimates that approximately 300,000 of those cannot be confidently classified as either benign or malignant through traditional histopathology methods. For these cases, the treatment plan can also be uncertain. Obtaining accurate, objective ancillary testing can mean the difference between a path of overtreatment or the risk of undertreatment. Interpreted in the context of other clinical, laboratory and histopathologic information, MyPath Melanoma is designed to reduce uncertainty and provide confidence for dermatopathologists and help dermatologists deliver more informed patient management plans.

More information about Castle's tests can be found at www.CastleTestInfo.com.

About Castle's Inflammatory Skin Disease Pipeline Test
Inflammatory skin disease accounts for a significant number of patient visits to both primary care and dermatology clinics across the United States every year. Psoriasis and atopic dermatitis are among the most common inflammatory skin conditions, and patient quality of life is severely impacted by these chronic diseases. Fortunately, systemic medications developed over the past 15 years have demonstrated a significant improvement in patients' lives. In the United States alone, there are about 18 million patients diagnosed with psoriasis and atopic dermatitis, and approximately 450,000 patients annually are eligible for these systemic therapies. While there are now many effective treatments options available for those with moderate-to-severe inflammatory skin diseases, current clinical practice relies on a trial-and-error approach for therapy selection. To answer this unmet clinical need, Castle Biosciences is developing a gene expression profile test to help guide systemic therapy selection for patients with moderate-to-severe psoriasis, atopic dermatitis and other related diseases.

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, Barrett's esophagus and mental health conditions. 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-UM, DecisionDx-PRAME, DecisionDx-UMSeq, TissueCypher and IDgenetix 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: our ability to improve the care of patients with skin cancers and inflammatory skin conditions through innovative tests that can guide more informed disease management decisions; the potential of DecisionDx-Melanoma test results to inform two clinical questions in the management of cutaneous melanoma: a patient's individual risk of SLN positivity and a patient's personal risk of melanoma recurrence and/or metastasis; the potential of DecisionDx-SCC test results to predict individual risk of cutaneous squamous cell carcinoma metastasis for patients with one or more risk factors; the potential of MyPath Melanoma to provide an accurate, objective result to aid dermatopathologists and dermatologists in characterizing difficult-to-diagnose melanocytic lesions; and the potential of our inflammatory skin disease pipeline test to help guide systemic therapy selection for patients with moderate-to-severe psoriasis, atopic dermatitis and other related diseases. 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, including with respect to the discussion of DecisionDx-Melanoma, DecisionDx-SCC, MyPath Melanoma and Castle's inflammatory skin disease pipeline test 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, 2022, our Quarterly Report on Form 10-Q for the three months ended June 30, 2023, 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.