Long-term Outcomes Data Shared at SSO 2024 Show That Patients with a Low-Risk DecisionDx-Melanoma Test Result Were Recurrence Free at Three Years, Including Those Who Utilized the Test to Help Guide the Decision to Avoid an SLNB

Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced that new data highlighting the performance of its DecisionDx-Melanoma test in predicting risk of sentinel lymph node (SLN) positivity in patients with CM is being presented at the Society of Surgical Oncology 2024 (SSO 2024) Annual Meeting, being held March 20-23 in Atlanta.

“We have previously demonstrated that our DecisionDx-Melanoma test identifies patients who are eligible for an SLNB but have less than a 5% likelihood of being SLN positive, and could therefore consider avoiding the procedure,” said Derek Maetzold, president and chief executive officer of Castle Biosciences. “We have also demonstrated that our test is a strong and independent predictor of metastasis. The study that was orally presented at SSO 2024 demonstrates that patients who did avoid an SLNB procedure had excellent outcomes to date. This demonstration is highly important as it showed that our test can help patients avoid an unnecessary procedure.”

DecisionDx-Melanoma is supported by 50 peer-reviewed publications involving more than 10,000 patient samples, demonstrating its robust value in guiding risk-aligned patient care. The test has been designed and validated to inform two clinical questions in the management of melanoma: a patient’s risk of melanoma recurrence and metastasis, and their individual risk of SLN positivity, as highlighted in Castle’s SSO 2024 abstracts outlined below.

DecisionDx-Melanoma

• Oral Presentation Number and Title: 62: Prospective validation of the i31-gene expression profile test for cutaneous melanoma to select patients who may consider foregoing sentinel lymph node biopsy
• Session: Melanoma Parallel Session
• Presenter and Lead Author: J. Michael Guenther, M.D., St. Elizabeth Physicians, Edgewood, Kentucky

Summary: This study shares three-year outcomes data from Castle’s prospective, multicenter study of patients with CM who were being considered for an SLNB (n=322). SLNB is an invasive surgical procedure used to determine whether a patient’s cancer has spread to nearby lymph nodes; the procedure returns a surgical result that is negative for metastasis in approximately 88% of patients. Current National Comprehensive Cancer Network guidelines use a 5% likelihood of SLN positivity as the threshold to avoid versus consider/recommend an SLNB due to an increased risk of metastasis. DecisionDx-Melanoma has been validated to provide a patient’s individualized risk of SLN positivity (i31-GEP for SLNB) by integrating clinical and pathologic risk factors with the patient’s tumor biology. In the study, no patients with a DecisionDx-Melanoma predicted risk of SLN positivity less than 5% had a positive SLN (among all tumor stages studied). If DecisionDx-Melanoma was used to inform management decisions, the test’s results could have further reduced the number of patients with T1-T2 tumors who could have avoided SLNB by 25%. Additionally, at three years, all patients with a low-risk DecisionDx-Melanoma test result were recurrence free (recurrence free survival of 100%). These data demonstrate that use of DecisionDx-Melanoma test results can guide accurate, risk-aligned clinical decision-making regarding the SLNB surgical procedure, within current guidelines. Further, the test can identify low-risk patients who can safely consider foregoing SLNB, thereby reducing unnecessary SLNB procedures (by approximately 25% in this study alone) and the associated costs and risks of complications that accompany them.