Castle Biosciences Presents Data at the 10th World Congress of Melanoma and 17th European Association of Dermato-Oncology Congress

Castle highlights its suite of skin cancer genomic tests

Castle Biosciences, Inc. (Nasdaq: CSTL), a skin cancer diagnostics company providing personalized genomic information to improve cancer treatment decisions, presented data on its three skin cancer gene expression profile tests at the 10th World Congress of Melanoma and 17^th European Association of Dermato-Oncology (EADO) Congress.

DecisionDx®-Melanoma:

DecisionDx-Melanoma is Castle’s gene expression profile test that uses an individual patient’s tumor biology to predict risk of cutaneous melanoma metastasis or recurrence, as well as sentinel lymph node (SLN) positivity, independent of traditional staging factors. Castle presented data on DecisionDx-Melanoma with two virtual posters. The first is a late-breaking abstract, titled “Integration of the 31-gene expression profile test with clinicopathologic features (i31-GEP) to assess sentinel lymph node positivity risk in patients with cutaneous melanoma.” More details can be found here in the Company’s news release from April 15, 2021.

A second poster entitled “Using a 31-gene expression profile test to stratify patients with sentinel lymph node negative stage I-II cutaneous melanoma according to recurrence risk: Longer-term follow-up from a prospective, multicentre study” was also presented. This poster can be found here.

Study methods and findings:

• Interim data from an independent, prospective multicentre Spanish cohort was previously published.
• This poster provided long-term performance data (median follow-up 3.9 years) of 86 primary melanoma tumors from patients staged I-II at diagnosis according to the American Joint Committee on Cancer (AJCC) 7^th edition criteria with negative SLN biopsy (SLNB) results, which were tested with DecisionDx-Melanoma.
• Significantly different risk profiles (p=0.005) with respect to disease-free survival (DFS) were maintained between groups with:
  • 3-year Disease-Free Survival for Class 1A = 100%
  • 3-year Disease-Free Survival for Class 1A, 1B/2A = 91%
  • 3-year Disease-Free Survival for Class 2B = 75%
• Patients with a DecisionDx-Melanoma Class 2B result had three times the odds of recurrence relative to those with a Class 1A result.
• Distant metastasis was not observed in the Class 1A group, while 75% occurred in the high-risk Class 2B group.
• The study authors conclude that DecisionDx-Melanoma significantly differentiates recurrence risk in SLN negative patients, which may allow for better resource allocation to patients at the highest risk of melanoma recurrence.

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. Castle presented data on DecisionDx-SCC with two virtual posters. Both posters highlight studies in which the 40-gene expression profile test demonstrated the ability to accurately classify risk for metastasis in SCC patients with one or more risk factors.

The first poster is entitled “Incorporation of a prognostic 40-gene expression profile (40-GEP) test into clinicopathological risk assessment using newly published guidelines for cutaneous squamous cell carcinoma (cSCC).” The poster can be found here.

Study methods and findings:

• The National Comprehensive Cancer Network (NCCN) published updated SCC guidelines in 2021, now categorizing local SCC into three groups: low risk, high risk and very high risk. This study was performed to assess the performance of DecisionDx-SCC within these new NCCN guidelines.
• 420 primary SCC archival tumor specimens with one or more associated risk factors and known three-year outcomes were collected, tested with DecisionDx-SCC and analyzed using Kaplan Meier and Cox multivariate regression analysis. All patients in this cohort were classified as high risk or very high risk by the new National Comprehensive Cancer Network (NCCN) framework.
• Importantly:
  • DecisionDx-SCC provided significant stratification within both the NCCN high-risk group (p=0.0001) and the NCCN very high-risk group (p<0.0001).
  • Multivariate Cox regression analysis showed that both the DecisionDx-SCC Class 2A (p<0.001) and Class 2B (p<0.001) were independent and stronger predictors of metastasis when compared to NCCN groups (Class 2A hazard ratio = 2.92; Class 2B hazard ratio = 9.50; NCCN very high-risk hazard ratio = 1.99).
• These data show that DecisionDx-SCC provides further stratification for the risk of metastasis within high-risk and very high-risk SCC sample groups.
• The study validated that DecisionDx-SCC adds independent prognostic value within the new NCCN guidelines and could be applied as an adjunct to enhance SCC risk stratification and found that incorporating DecisionDx-SCC into SCC patient risk assessment could lead to more personalized and risk-appropriate pathways for improvement of patient management and disease related outcomes.

The second DecisionDx-SCC poster is entitled “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.” The poster can be found here .

Study methods and findings:

• 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:
  • 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.
  • Technical reliability of DecisionDx-SCC was 96.3%.
  • Most tested patients had three or more risk factors.

DecisionDx® DiffDx™-Melanoma:

DecisionDx DiffDx-Melanoma is designed to aid dermatopathologists in characterizing difficult-to-diagnose melanocytic lesions. DecisionDx DiffDx-Melanoma classifies these lesions as benign, intermediate-risk or malignant.

Two virtual posters highlighted studies in which DecisionDx DiffDx-Melanoma demonstrated the ability to refine diagnoses of difficult-to-diagnose melanocytic lesions.

The first poster is entitled “Performance of a diagnostic 35-gene expression profile test (GEP) on difficult-to-diagnose melanocytic lesions.” The poster can be found here.

Study methods and findings:

• DecisionDx DiffDx-Melanoma’s performance was evaluated in its target difficult-to-diagnose population, which included lesions of unknown malignant potential (UMP) and diagnostically discordant lesions.
• In a cohort of 65 difficult-to-diagnose melanocytic lesions, the test provided a result in 100% of lesions, (i.e., no technical failures).
• DecisionDx DiffDx-Melanoma provided an actionable result in 97% of these difficult-to-diagnose lesions, as only 2 cases received an intermediate result.
• DecisionDx DiffDx-Melanoma’s previously published accuracy metrics in lesions with diagnostic concordance has been shown to alleviate uncertainty in difficult-to-diagnose lesions leading to recommendations for decreased unnecessary procedures while appropriately identifying at-risk patients.

The second DecisionDx DiffDx-Melanoma poster is entitled “Development, Validation, and Clinical Utility of the 35-Gene Expression Profile Test for Use as an Adjunctive Melanoma Diagnostic Tool.” The data therein was previously published in SKIN: The Journal of Cutaneous Medicine. The poster can be found here.

Study methods and findings:

• DecisionDx DiffDx-Melanoma was developed using artificial intelligence methods trained on 200 benign nevi and 216 melanomas to select a panel of 32 discriminant and 3 control genes.
• The test’s ability to differentiate accurately between benign and malignant pigmented skin lesions was characterized.
• The test provides a modest intermediate-risk zone of 3.6% and a high technical success rate at 96.6%.
• The analytical validity data of the DecisionDx DiffDx-Melanoma test demonstrates high precision as an indication of technical success.
• Dermatopathologists utilized the DecisionDx DiffDx-Melanoma result to refine their diagnoses and their diagnostic confidence increased by 51%.
• Dermatologists utilized the DecisionDx DiffDx-Melanoma result, which led to altered treatment plans including re-excisions in agreement with the DecisionDx DiffDx-Melanoma result.

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 December 31, 2020, DecisionDx-Melanoma has been ordered more than 68,920 times for use in patients with cutaneous melanoma.

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

About DecisionDx DiffDx-Melanoma

DecisionDx® DiffDx™-Melanoma is designed to aid dermatopathologists in characterizing difficult-to-diagnose melanocytic lesions. Of the approximately 2 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. DecisionDx DiffDx-Melanoma classifies these lesions as: benign (gene expression profile suggestive of benign neoplasm); intermediate-risk (gene expression profile cannot exclude malignancy); or malignant (gene expression profile suggestive of melanoma). Interpreted in the context of other clinical, laboratory and histopathologic information, DecisionDx DiffDx-Melanoma is designed to add diagnostic clarity and confidence for dermatopathologists while helping dermatologists deliver more informed patient management plans.

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, 2A or 2B 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 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), cutaneous squamous cell carcinoma (DecisionDx®-SCC), suspicious pigmented lesions (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. 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-SCC, 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 differentiate the risk of recurrence in SLN negative patients and provide better resource allocation to patients at the highest risk of melanoma recurrence; statements concerning the ability of DecisionDx DiffDx-Melanoma to refine diagnoses of difficult-to-diagnose melanocytic lesions and alleviate uncertainty in difficult-to-diagnose lesions and lead to recommendations for decreased unnecessary procedures while appropriately identifying at-risk patients. ; and statements concerning the ability of DecisionDx-SCC test results to accurately classify and predict the risk for metastasis in SCC patients with one or more risk factors, add independent prognostic value within the new NCCN guidelines, apply as an adjunct to enhance cSCC risk stratification and lead to more personalized and risk-appropriate pathways for improvement of patient management and disease related outcomes. 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, our products’ ability to provide the aforementioned benefits to patients and the risks set forth in our Annual Report on Form 10-K for the year ended December 31, 2020, 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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