Castle Biosciences Presents Data on DecisionDx®-Melanoma and DecisionDx®-SCC at the DERM2021 NP/PA CME Conference

Castle Biosciences, Inc. (Nasdaq: CSTL), a dermatologic diagnostics company providing personalized genomic information to inform treatment decisions, today announced data presentations on two of its skin cancer gene expression profile tests at the DEF (Dermatology Education Foundation) Essential Resource Meeting (DERM2021) NP/PA (Nurse Practitioner/Physician Assistant) CME Conference, taking place from Aug. 5-8, 2021.

DecisionDx®-Melanoma:

DecisionDx-Melanoma is Castle’s gene expression profile test that uses an individual patient’s tumor biology to predict the risk of cutaneous melanoma metastasis or recurrence, as well as sentinel lymph node (SLN) positivity, independent of traditional staging factors. The Company will present two posters that highlight data assessing the clinical utility of the DecisionDx-Melanoma test.

The first poster, titled “Clinical utility of the 31-gene expression profile test on the management of cutaneous melanoma by nurse practitioners and physician assistants,” highlights nurse practitioners’ and physician assistants’ (NP/PAs) attitudes toward the clinical use of DecisionDx-Melanoma in patients diagnosed with cutaneous melanoma.

Study methods and findings:

• In 2020, an institutional review board (IRB)-approved, 20-question study was conducted to understand the perception and clinical use of DecisionDx-Melanoma by clinicians, including NP/PAs.
• Of the 711 survey respondents, 266 self-identified as NP/PAs, with 50% of those (n=133) reporting ordering DecisionDx-Melanoma within the previous year.
• 89% of the NP/PAs responded that comprehensive prognostic testing (including DecisionDx-Melanoma) could improve patient care.
• Most NP/PAs who use DecisionDx-Melanoma (97%) would recommend additional prognostic testing to close friends or family members compared to just 58% of those who do not use DecisionDx-Melanoma.
• Among the NP/PAs who ordered DecisionDx-Melanoma in the previous year:
  • 99% would recommend the test to a colleague.
  • Most would consider patient management changes for patients with a T1 tumor (82%) or stage I melanoma (81%) who received a high-risk Class 2B DecisionDx-Melanoma test result.

The second poster is entitled “Integration of the continuous 31-gene expression profile score and clinicopathologic features to predict sentinel lymph node status in patients with cutaneous melanoma: Use of artificial intelligence to attain near perfect prediction.” The study highlights the use of artificial intelligence to combine patients’ clinical and pathological information with DecisionDx-Melanoma to improve the precision of sentinel lymph node (SLN) positivity prediction.

Study methods and findings:

• An integrated DecisionDx-Melanoma test result (i31-GEP) was developed to integrate DecisionDx-Melanoma’s output, a risk assignment based on gene expression profile analysis, with clinicopathologic risk factors.
• The DecisionDx-Melanoma test result was the most important variable in predicting SLN positivity in relation to the other included variables.
• The independent validation phase showed that the i31-GEP provides a highly concordant prediction of SLN positivity rate compared to observed rates (linear regression slope of 0.999, with 1.0 representing complete concordance).
• Of patients originally classified with 5-10% SLN positivity risk by current guidelines, DecisionDx-Melanoma reclassified 63% of those patients, whose actual risk of SLN positivity was less than 5% or greater than 10%.
• i31-GEP had a high negative predictive value of 98% in patients with T1-T4 tumors.

DecisionDx®-SCC:

DecisionDx-SCC is Castle’s prognostic gene expression profile test for patients diagnosed with high-risk cutaneous squamous cell carcinoma (SCC), designed to use a patient’s tumor biology to predict individual risk of metastasis for patients with SCC and one or more risk factors. Two posters highlight data assessing the clinical utility of the DecisionDx-SCC test.

The first poster, titled “Real-world clinical usage data demonstrates appropriate utilization of the prognostic 40-gene expression profile test for cutaneous squamous cell carcinoma with one or more risk factors,” highlights the importance of utilizing DecisionDx-SCC test results in clinical assessments with traditional clinicopathologic risk factors for improved stratification of high-risk SCC patients.

Study methods and findings:

• The objective of the study was to demonstrate the independent prognostic value of DecisionDx-SCC within existing risk assessment methods and report on the early clinical usage of DecisionDx-SCC.
• Summary metrics were generated on the first 1000 samples received for DecisionDx-SCC testing that met clinical testing criteria. Metrics on early clinical usage include:
  • The technical reliability of DecisionDx-SCC was 96.3%.
  • 69.0% of samples received DecisionDx-SCC Class 1 results, 26.0% received DecisionDx-SCC Class 2A results and 1.3% received DecisionDx-SCC Class 2B results.
  • 52% of tested patients had three or more risk factors.

• This study demonstrated that the intended use population (high-risk SCC patients with one or more risk factors) aligns with the cases that were submitted for clinical testing.
• The study also found that DecisionDx-SCC results can be applied as an adjunct to enhance SCC risk stratification and contribute to risk-appropriate surveillance and treatment decisions.

The second poster is entitled “Clinical utility of the 40-gene expression profile (40-GEP) for improved patient management decisions when combined with current clinicopathological risk factors for cutaneous squamous cell carcinoma (cSCC): Case Series.” The study highlights the significance of integrating novel molecular prognostication with traditional clinicopathological risk factors to inform selection of risk-appropriate treatment and surveillance strategies for high-risk SCC patients through two specific case reports.

Study methods and findings:

• Case #1 and Case #2 were identically staged using two formal staging systems; both were male immunocompromised patients, with similarly sized, poorly differentiated tumors located on the left temple where Mohs surgery was completed.
• Case #1 declined further treatment and was recurrence free. A retrospective analysis of the initial biopsy with DecisionDx-SCC highlighted a biologically less aggressive tumor (Class 1).
• Case #2 presented with metastatic SCC 3 months after Mohs surgery and later died from SCC. A retrospective analysis of the initial biopsy with DecisionDx-SCC highlighted a biologically aggressive tumor (Class 2B).
• These findings demonstrate the utility of the 40-GEP test as an adjunct to enhance cSCC risk stratification.

About DecisionDx-Melanoma

DecisionDx®-Melanoma is a gene expression profile test that uses an individual patient’s tumor biology to predict individual risk of cutaneous melanoma metastasis or recurrence, as well as sentinel lymph node positivity, independent of traditional staging factors, and has been studied in more than 5,700 patient samples. Using tissue from the primary melanoma, the test measures the expression of 31 genes. The test has been validated in four archival risk of recurrence studies of 901 patients and six prospective risk of recurrence studies including more than 1,600 patients. To predict likelihood of sentinel lymph node positivity, the Company utilizes its proprietary algorithm, i31-GEP, to produce an integrated test result. i31-GEP is an artificial intelligence-based neural network algorithm (independently validated in a cohort of 1,674 prospective, consecutively tested patients with T1-T4 cutaneous melanoma) that integrates the DecisionDx-Melanoma test result with the patient’s traditional clinicopathologic features. Impact on patient management plans for one of every two patients tested has been demonstrated in four multicenter and single-center studies including more than 560 patients. The consistent performance and accuracy demonstrated in these studies provides confidence in disease management plans that incorporate DecisionDx-Melanoma test results. Through March 31, 2021, DecisionDx-Melanoma has been ordered more than 73,396 times for use in patients with cutaneous melanoma.

More information about the test and disease can be found at www.CastleTestInfo.com.

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), 2A (moderate) or 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.

More information about the test and disease can be found at www.CastleTestInfo.com.

About Castle Biosciences

Castle Biosciences (Nasdaq: CSTL) is a commercial-stage dermatologic diagnostics 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), cutaneous squamous cell carcinoma (DecisionDx®-SCC), suspicious pigmented lesions (myPath® Melanoma, DecisionDx® DiffDx™-Melanoma) and uveal melanoma (DecisionDx®-UM, DecisionDx®-PRAME and DecisionDx®-UMSeq). For more information about Castle’s gene expression profile tests, visit www.CastleTestInfo.com.

Castle also has active research and development programs for tests in other dermatologic 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. Castle Biosciences is based in Friendswood, Texas (Houston), and has laboratory operations in Phoenix. Additionally, in May of 2021, Castle acquired the myPath Melanoma laboratory in Salt Lake City.

For more information, visit www.CastleBiosciences.com.

DecisionDx-Melanoma, DecisionDx-CMSeq, DecisionDx-SCC, myPath Melanoma, DecisionDx DiffDx-Melanoma, 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 DecisionDx-Melanoma’s ability to improve patient care and outcomes, guide and change cancer management decisions and provide a highly concordant prediction of SLN positivity rate compared to observed rates, and DecisionDx-SCC’s ability to enhance SCC risk stratification and contribute to risk-appropriate surveillance and treatment decisions. 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 effects of the COVID-19 pandemic on our business and our efforts to address its impact on our business, subsequent study results and findings that contradict earlier study results and findings, DecisionDx-Melanoma’s and DecisionDx-SCC’s ability to provide the aforementioned benefits to patients and the risks set forth in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, 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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