Clinical Utility of Belay Summit™ Cerebrospinal Fluid Test to Inform Diagnosis and Management of Central Nervous System Cancer—A Single Institution Case Series

Background: Cytology from cerebrospinal fluid (CSF) is standard-of-care to detect central nervous system (CNS) cancers but suffers from low-sensitivity and lacks associated molecular information, often requiring brain biopsy or resection to obtain. Belay Diagnostics offers analytically and clinically validated CSF-based tests to support the diagnosis and management of primary and secondary CNS cancers. However, the clinical utility (CU) of these assays has not been previously evaluated. Methods: This retrospective study presents a real-world, single institution experience of using the Belay Summit liquid biopsy test for all orders received (n = 123) between October 2024 and September 2025. Clinical information was reviewed for demographics, provisional diagnosis, oncology history, CSF cytology results, and tumor genomic profiling results. The primary endpoint of this study was to evaluate the impact of Belay CSF-based assays on physician diagnosis and treatment decisions. Secondary endpoints included evaluating the clinical performance of the Belay Summit test verses cytology in CNS malignancy detection (sensitivity, specificity, and accuracy). Results: The cohort included 120 patients with suspected or previously diagnosed primary (n = 40) or metastatic (n = 80) CNS tumors; three patients completed longitudinal testing for a total of 123 specimens and test orders. Summit showed higher sensitivity for CNS malignancy (90%) over CSF cytology (12%). The Belay CSF liquid biopsy test demonstrated strong clinical utility and was essential to clinical course pursued in 93% (114/123) of specimens, informing treatment and management decisions. Conclusions: The Belay Summit test provides clinically meaningful information to support physician decision-making for the diagnosis and management of primary and secondary CNS tumors, especially in cases where tissue sampling is infeasible.