Castle Biosciences Announces Study Establishing the Value of Integrating DecisionDx-SCC Test into Management of High-Risk Cutaneous Squamous Cell Carcinoma

Data presented at the 2020 Winter Clinical Dermatology Conference

Castle Biosciences, Inc. CSTL, a skin cancer diagnostics company providing personalized genomic information to improve cancer treatment decisions, today announced the presentation of clinical utility data for its cutaneous squamous cell carcinoma (SCC) prognostic test, DecisionDx^®-SCC, for patients diagnosed with high-risk cutaneous SCC. The test is expected to be launched commercially in the second half of 2020.

The poster titled, "Integrating the 40-Gene Expression Profile (40-GEP) Test into Management of High-Risk Cutaneous Squamous Cell Carcinoma," was presented during the 2020 Winter Clinical Dermatology Conference, January 17-22 in Hawaii.

The data presented support a framework for integration of DecisionDx-SCC into risk-appropriate management of high-risk cutaneous SCC patients (as defined by the National Comprehensive Cancer Network [NCCN]).

Disease and Study Background

• Approximately 1 million patients are diagnosed with cutaneous SCC in the U.S. each year, and the incidence continues to grow.
• As with other cancer types, NCCN guidelines define treatment pathways based on risk of metastasis. In the case of cutaneous SCC, there are two clinicopathologically defined categories: low-risk and high-risk.
• The Company believes two important issues exist in implementing a high-risk treatment pathway. First, the NCCN risk criteria, as well as available staging systems, have low positive predictive value (PPV) – meaning that the majority of high-risk patients do not develop metastasis; and, second, the high-risk treatment pathways are broad.
• The clinical implication being that many patients categorized as high risk, but who have a low biological risk of metastasis, may be overtreated with radiation, chemotherapy or other interventions; and those patients categorized as high risk and who also have a high biological risk of metastasis may be undertreated if clinical decisions are to follow a conservative treatment plan within the broad boundaries of NCCN high-risk pathways.
• The Company believes improved stratification for implementation of risk-appropriate treatment plans for patients within NCCN-defined high-risk cutaneous SCC is needed. NCCN defines high risk as cutaneous SCC patients with a single high-risk feature, e.g., immunodeficiency; tumor diameter greater than or equal to 2cm; any tumor of the mask area, genitals, hands, or feet; or poor tumor differentiation.
• DecisionDx-SCC was developed and validated to stratify risk of regional or distant metastasis at three years after diagnosis in high-risk cutaneous SCC patients, classifying patients as low (Class 1), high (Class 2A) or highest (Class 2B) risk of metastasis.
• This study was designed to evaluate the integration of DecisionDx-SCC (40-GEP test) with AJCC and Brigham and Women's Hospital (BWH) T stage criteria into management of 300 NCCN high-risk cutaneous SCC patients.
• Within the broad framework of NCCN recommendations for high-risk cutaneous SCC, the aim is to identify those high-risk patients who would be eligible for a conservative, reduced treatment plan, thus avoiding unnecessary adjuvant interventions, and identifying those patients who would most benefit from aggressive adjuvant treatment strategies.

Study Findings

• Integration of DecisionDx-SCC for NCCN-defined high-risk cutaneous SCC patients with T staging identified a group of 159 patients (Class 1, T1-T2) with a 7.5% rate of metastasis, which approaches that of the general cutaneous SCC patient population. A low intensity management strategy, within the broad NCCN high-risk guidelines, could spare this patient group unnecessary adjuvant procedures and potential adverse effects.
• Conversely, those patients (n=24) with rates of metastasis surpassing 50% (Class 2B), regardless of AJCC or BWH T stage, would warrant a high intensity strategy, also within the broad NCCN high-risk guidelines, that increases follow-up visits, utilizes imaging and/or biopsies for nodal assessment, and offers adjuvant treatments and clinical trials for probable metastatic events.
• The data support a framework for risk-aligned treatment plans when DecisionDx-SCC is incorporated into management of NCCN high-risk cutaneous SCC patients.

"There is a clear need to improve identification of true high-risk and lower-risk patients diagnosed with high-risk cutaneous SCC, so that risk-directed treatment plans can be implemented," said Aaron Farberg, M.D., study investigator, Icahn School of Medicine at Mount Sinai, New York and Arkansas Dermatology Skin Cancer Center, Little Rock, Arkansas. "Clinical use of DecisionDx-SCC, along with current staging systems, may better identify patients with cutaneous SCC at high risk for metastasis and enable more informed clinical decisions regarding adjuvant therapy and other management options."

The DecisionDx-SCC test is the second skin cancer test discovered, developed and validated by Castle Biosciences.

About Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (SCC), a nonmelanoma skin cancer, is one of the most common cancers. Approximately 1,000,000 patients are diagnosed with cutaneous SCC each year in the U.S. Most patients have a favorable prognosis, but a subset of patients will develop metastasis, and up to 15,000 patients each year die from their disease, exceeding the number of deaths from cutaneous melanoma. As current staging parameters have a low positive predictive value, many more patients are considered high risk than actually develop metastatic disease. Conversely, many patients who develop metastatic disease are misidentified as low risk. This may lead to over and undertreatment of a substantial number of cutaneous SCC patients. To address this clinical need, Castle Biosciences has developed a gene expression profile test designed to improve upon current staging systems and identify patients with cutaneous SCC at high risk for metastasis or recurrence, in order to enable more informed clinical decisions regarding adjuvant therapy and other management options.

About Castle Biosciences

Castle Biosciences CSTL is a commercial-stage dermatologic cancer 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; www.SkinMelanoma.com) and uveal melanoma (DecisionDx^®-UM, DecisionDx^®-PRAME and DecisionDx^®-UMSeq; www.MyUvealMelanoma.com), with products in development for other underserved cancers, the two most advanced of which are focused on patients with cutaneous squamous cell carcinoma, and patients who have a difficult-to-diagnose pigmented lesion. Castle Biosciences is based in Friendswood, Texas (Houston), and has laboratory operations in Phoenix, Arizona. For more information, visit www.CastleBiosciences.com.

DecisionDx-Melanoma, DecisionDx-CMSeq, 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 the ability of DecisionDx-SCC test results to appropriately direct cutaneous SCC patient work-up and treatment plans; the ability of DecisionDx-SCC to improve upon existing staging systems and accurately classify patient risk; and expectations of DecisionDx-SCC to enable de-escalation of care in patients identified as high risk by traditional staging and provide objective data to implement proper recommendations for actual high-risk patients. 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 risks set forth in our final prospectus filed with the SEC on July 26, 2019 relating to our Registration Statements on Form S-1 (File Nos. 333-232369 and 333-232796) and our Quarterly Report on Form 10-Q for the quarter ended September 30, 2019, filed with the SEC on November 12, 2019, 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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