Castle Biosciences Presents Data on DecisionDx-Melanoma at the Virtual European Association of Dermato-Oncology (EADO) Congress

Castle Biosciences, Inc. (Nasdaq: CSTL), a skin cancer diagnostics company providing personalized genomic information to improve cancer treatment decisions, today announced the presentation of data demonstrating that DecisionDx®-Melanoma identifies patients with T1-T2 melanoma who have a low risk of sentinel lymph node (SLN) positivity. DecisionDx-Melanoma is Castle's 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 SLN positivity. The findings were highlighted in a poster presentation at the 16^th European Association of Dermato-Oncology (EADO) Congress, being held virtually Oct.12-14, 2020.

"Only 12% of patients who undergo sentinel lymph node biopsy surgery (SLNB) have a positive result," said Bob Cook, Ph.D., senior vice president of research and development at Castle Biosciences and lead author on the study. "While the likelihood of SLN-positivity decreases with age, the risk of death from melanoma increases. Our study findings demonstrate that DecisionDx-Melanoma, combined with T stage, can help identify patients 65 years of age and older with a low probability of SLN-positivity. Therefore, DecisionDx-Melanoma can provide clinicians and patients with additional, objective data and help inform decisions on SLNB surgery, helping avoid unnecessary procedures and potentially reducing healthcare costs."

The study's objective was to incorporate DecisionDx-Melanoma with clinical features to identify patients with T1-T2 melanoma likely to have low SLN-positivity rates. The poster, entitled "Identification of patients with T1-T2 melanoma and low risk of sentinel lymph node positivity using a 31-gene expression profile test," highlights the use of DecisionDx-Melanoma in combination with clinical features. The SLN status of 2,303 patients diagnosed with T1-T2 melanoma were analyzed, and DecisionDx-Melanoma was used to stratify patient risk into low (Class 1A), intermediate (Class 1B/2A) and high (Class 2B) risk.

Key findings include:

• For patients 65 years of age or older with T1-T2 tumors (n = 1,047), a positive SLN was observed in only 1.8% (95% CI 0.9-3.1) of clinically and pathologically assessed patients identified as lowest risk (Class 1A) by DecisionDx-Melanoma, versus 14.6% (95% CI 9.0-21.9) of patients identified as high risk (Class 2B).
• Class 1A results were associated with higher rates of 3-year overall survival and metastasis-free survival.

Medicare Administrative Contractor, Palmetto GBA MolDx, recently issued a final expanded local coverage determination for DecisionDx-Melanoma, expanding Medicare coverage for the test in cutaneous melanoma.

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. Prediction of the likelihood of sentinel lymph node positivity has also been validated in two prospective multicenter studies that included more than 3,000 patients. 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 June 30, 2020, DecisionDx-Melanoma has been ordered more than 59,900 times for use in patients with cutaneous melanoma.

More information about the test and disease can be found at www.SkinMelanoma.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; www.SkinMelanoma.com), cutaneous squamous cell carcinoma (DecisionDx^®-SCC, www.MySCCSkinCancer.com) and uveal melanoma (DecisionDx^®-UM, DecisionDx^®-PRAME and DecisionDx^®-UMSeq; www.MyUvealMelanoma.com). Castle also has products in development for other underserved cancers, the most advanced of which is focused on 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-SCC, DecisionDx-UM, DecisionDx-PRAME and DecisionDx-UMSeq and 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-Melanoma test results to help identify patients with low probability of sentinel lymph node positivity, optimize or improve treatment decisions and reduce healthcare costs. 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, changes in the competitive landscape and the introduction of competitive products, changes in local coverage determinations, the impact of the COVID-19 pandemic on our business and results of operations, as well as the other risks set forth in our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 10, 2020, our Quarterly Report on Form 10-Q for the quarter ended June 30, 2020, filed with the SEC on August 10, 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.