ctDNA-Guided Intraventricular Therapy for CNS Malignancies

This prospective, single-center study will evaluate whether cerebrospinal fluid (CSF) circulating tumor DNA (ctDNA) testing using the Belay Summit assay can improve the clinical management of patients with malignant gliomas or brain metastases from non-small cell lung cancer (NSCLC) or breast cancer who are suspected of having central nervous system (CNS) disease. Patients undergoing clinically indicated CSF evaluation will receive standard clinical testing, including CSF cytology and the Belay Summit ctDNA assay. Treatment decisions will remain at the discretion of the treating multidisciplinary neuro-oncology team. The primary objective is to evaluate 6-month clinical CNS progression-free survival (cCNS-PFS), with secondary objectives assessing safety and the association between CSF ctDNA dynamics and clinical outcomes. Exploratory proteogenomic analyses will be performed on residual CSF specimens when sufficient sample is available.