New Data from DECIDE Study Show the Significant Role of DecisionDx®-Melanoma Test Results and Patient Preference in Decisions to Perform the Sentinel Lymph Node Biopsy (SLNB) Surgical Procedure

Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced new data from its prospective, multicenter DECIDE¹ study in which DecisionDx®-Melanoma test results influenced 85% of clinicians' decisions regarding the sentinel lymph node biopsy (SLNB) surgical procedure, demonstrating the role of the test's results in guiding risk-aligned patient management decisions.

"Melanoma is an aggressive and deadly disease, thus any decisions on whether to forego a procedure like an SLNB cannot be taken lightly," said J. Michael Guenther, M.D., surgical oncologist at St. Elizabeth Physicians in Edgewood, Kentucky. "The clinically actionable information that DecisionDx-Melanoma provides is precious to both doctors and patients. It enables me to have more productive conversations with my patients, so we can make shared, informed decisions about their overall care; this includes decisions on whether to pursue an SLNB if their risk of a positive sentinel lymph node is low."

The data was presented during the 19th International Congress of the Society for Melanoma Research (SMR), held Oct. 17-20 in Edinburgh, United Kingdom, through a poster (# P- 037) titled, "Clinical use of the 31-gene expression profile for informing sentinel lymph node biopsies: a prospective, multicenter study." The poster can be viewed here.

SLNB surgery is used to determine whether a patient's melanoma has spread to the lymph node; the procedure has the potential for complications and returns a biopsy that is negative for metastatic spread in up to 88% of patients who undergo the procedure.^2-3 DecisionDx-Melanoma is a gene expression profile risk stratification test 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. The test has been validated to identify patients who have less than a 5% risk of a positive SLN, indicating that these patients could safely forego the SLNB surgical procedure, and improve the yield of positive SLNBs by identifying patients more likely to have a positive SLNB result.^4-5

Study highlights:

• The prospective, multicenter study included patients with invasive cutaneous melanoma (tumors staged as T1a (and at least one high-risk feature), T1b and T2) who were considering the SLNB surgical procedure.
• Clinicians received DecisionDx-Melanoma test results prior to making SLNB decisions and were asked which features influenced their decision on whether to perform the procedure. Potential influencing factors included patient preference, clinical and pathological features and DecisionDx-Melanoma results.
• The data showed that DecisionDx-Melanoma test results influenced 85% of SLNB decisions, and that DecisionDx-Melanoma test results and patient preference played a significant role in influencing the decision to undergo or forego SLNB.
  • When DecisionDx-Melanoma test results influenced for SLNB, the procedure was performed in 92% of the cases in the study; similarly, when the test result influenced against SLNB, the decision was made to forego SLNB in 70% of cases. This data indicates that the test's results in conjunction with current guidelines can guide risk-aligned clinical decision-making regarding the SLNB surgical procedure.
• The use of DecisionDx-Melanoma test results in conjunction with current guidelines resulted in a significant reduction of SLNB procedures performed, most notably a 29% decrease in SLNBs performed for patients with a low-risk (Class 1A) test result, compared to SLNB decisions made based on a patient's clinicopathologic risk factors alone (p<0.01).

As demonstrated in the study, DecisionDx-Melanoma test results can influence important clinical decisions regarding the SLNB surgical procedure. Additionally, the use of DecisionDx-Melanoma test results could help patients with low-risk (Class 1A) test results, whose tumor biology indicates that they can safely forego the procedure and still experience positive outcomes, and their clinicians have more informed conversations regarding clinical decisions and avoid a potentially unnecessary procedure.

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 9,000 patient samples. DecisionDx-Melanoma's clinical value is supported by more than 35 peer-reviewed and published studies, providing confidence in disease management plans that incorporate the test's results. Through June 30, 2022, DecisionDx-Melanoma has been ordered 105,239 times for patients diagnosed 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, 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, DiffDx-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: the potential of DecisionDx-Melanoma test results, in conjunction with current guidelines, to reduce the number of SLNB procedures performed, particularly in patients with a low biological risk of metastasis; guide and influence important clinical and risk-aligned patient management decisions regarding the SLNB surgical procedure; enable clinicians and their patients to have more productive conversations and make shared, informed decisions about the patient's overall care; identify patients who could safely forego the SLNB surgical procedure and improve the yield of positive SLNBs by identifying patients more likely to have a positive SLNB; and help patients with low-risk (Class 1A) test results, whose tumor biology indicates that they can safely forego the procedure and still experience positive outcomes, and their clinicians have more informed conversations regarding clinical decisions and avoid a potentially unnecessary procedure. The words "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 this study, including with respect to the discussion of DecisionDx-Melanoma 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 Quarterly Report on Form 10-Q for the three months ended June 30, 2022, 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.

1. DECIDE: DecisionDx-Melanoma Impact on Sentinel Lymph Node Biopsy Decisions and Clinical Outcomes
2. Huang H, Fu Z, Ji J, et al. Predictive Values of Pathological and Clinical Risk Factors for Positivity of Sentinel Lymph Node Biopsy in Thin Melanoma: A Systematic Review and Meta-Analysis. Front Oncol. 2022;12:817510. Published 2022 Jan 27. doi:10.3389/fonc.2022.817510
3. Moody JA, Ali RF, Carbone AC, et al. Complications of sentinel lymph node biopsy for melanoma - A systematic review of the literature. Eur J Surg Oncol. 2017;43(2):270-277. doi:10.1016/j.ejso.2016.06.407
4. Vetto JT, Hsueh EC, Gastman BR, et al. Guidance of sentinel lymph node biopsy decisions in patients with T1-T2 melanoma using gene expression profiling. Future Oncol. 2019;15(11):1207-1217. doi:10.2217/fon-2018-0912
5. Whitman ED, Koshenkov VP, Gastman BR, et al. Integrating 31-gene expression profiling with clinicopathologic features to optimize cutaneous melanoma sentinel lymph node metastasis prediction. JCO Precis Oncol. 2021;5:1466-79. doi:10.1200/PO.21.00162