Path-01. comparative evaluation of the diagnostic and prognostic performance of cnside™ versus standard cytology for leptomeningeal disease

OBJECTIVE We compared the real-world performance of the cerebrospinal fluid (CSF) CNSide™ versus cytology assays in diagnosing leptomeningeal disease (LMD). METHODS Consecutive patients with suspected LMD from January 2020 to December 2022 who underwent lumbar punctures for CSF cytology and CNSide™ analyses were reviewed. LMD diagnosis was defined by EANO criteria. We used descriptive statistics, confusion matrix, Kaplan Meier curves, and Cox proportional regression methods to analyze outcomes. RESULTS 87 patients with median age of 63 years (range:23-93) were evaluated, of which 82 (94%) met EANO positive (possible, probable, or confirmed criteria) cohort. Of the EANO cohort, 33 (40%) had uncontrolled systemic disease and 25 (46%) were on systemic therapy with medium/high CNS penetrance. The median time from initial cancer diagnosis to LMD was 31 months (range:21-43). LMD was diagnosed by CSF cytology (EANO confirmed) in 23 cases, all identified by CNSide™. CNSide™ identified an additional 13 cases, increasing diagnostic yield by 56.5%. Commonest primary histologies in the EANO cohort were breast (36, 44.0%) and lung (34, 41.5%); 18 (53.0%) of lung cancers harbored actionable molecular alterations, while breast cancers expressed hormone receptors in 27 (75%) and HER2 alterations in 8 (22%). Median overall survival (OS) for the CNSide™ cohort was 19.5 weeks (95%CI:11.0-28.0) and 31 weeks (95%CI:21-43) for EANO positive cases. Median OS for breast patients in CNSide™ cohort was 42 (R: 15-65) weeks, about 7-fold that of lung (median 6.5, R: 2-20). There was no correlation between OS and cell density by CNSide™ (HR:1.000, 95%CI:0.999-1.001, p=0.909). OS was higher for cases treated with intrathecal chemotherapy (HR:0.189, 95%CI:0.053-0.672, p=0.010), but not statistically different by radiotherapy modality (HR, 0.583, 95%CI:0.264-1.287, p=0.181). CONCLUSIONS This retrospective, single-institution, real-world analysis of CNSide™ showed increased sensitivity versus cytology and provided clinically relevant, cell-based molecular CSF analyses.