LMD-15. Beyond cytologY - A single institution experience using CNSide(TM) for diagnosing and monitoring treatment response in Non-Small Cell Lung Cancer patients with Leptomeningeal Carcinomatosis (LMC)

INTRODUCTION: Leptomeningeal Carcinomatosis (LMC) occurs in 3–9% of Non-Small Cell Lung Cancer (NSCLC) patients. Diagnosis of LMC includes clinical evaluation, imaging, and cytology. These have modest sensitivity and are inadequate for monitoring treatment response. Biocept’s CNSide(TM) is a proprietary assay utilizing a 10-antibody capture cocktail with microfluidic chamber that quantitatively detects tumor cells in the cerebrospinal fluid (CSF). Switch Blocker(TM) is a proprietary single gene assay that detects actionable mutations in the CSF. We describe a retrospective single institution experience using these assays in NSCLC patients with confirmed LMC or suspected LMC, treated between 2017 and 2021. METHODS: For fresh samples, CNSide and cytology were used to detect tumor cells, NGS and Switch Blocker was used to detect actionable mutations. Frozen samples were analyzed by NGS and/or Switch Blocker assays. RESULTS: CSF was collected from 30 samples (16 unique patients), of which frozen (8 unique patients) and fresh samples (8 unique patients; 5 with and 3 without LMC). CNSide detected tumor cells in 100% samples (10/10) vs cytology in 40% samples (4/10). Of those without LMC, neither CNSide nor cytology identified tumor cells. In patients with serial samples, CNSide tracked the clinical course. Analysis of frozen CSF by NGS identified mutations including EGFR in six (6), ALK in three (3) and BRAF in one (1) patient, which correlated with the primary tumor. The median survival from diagnosis of LMC for those with frozen samples was 71.6 weeks. CONCLUSION: We demonstrate that 1) survival of patients with LMC can be prolonged, especially when an actionable target is identified, 2) CNSide has greater sensitivity in detecting LMC than cytology, and 3) quantitative monitoring of CSF tumor cells can be used to guide initial and subsequent therapies. Larger clinical trials are needed to better establish the utility of CNSide in managing LMC.