Abstract 2296: Liquid biopsy of cerebrospinal fluid in breast to brain metastases

Abstract Up to 30% of patients with breast cancers will develop brain metastases, and this risk is especially high with HER2-positive cancers. For patients with central nervous system metastases, cerebrospinal fluid (CSF) liquid biopsies are a promising opportunity to monitor disease, inform treatment, and predict prognosis. This study explores the CSF liquid biopsy analytes from 3 patients with central nervous system metastases analyzed with the third generation non-enrichment high-definition single cell assay (HDSCA3.0) workflow. The detection of cellular analytes was compared between the CSF and matched peripheral blood (PB) samples. Circulating tumor cells (CTCs) were detected in the CSF but not the PB and were subsequently molecularly characterized by single cell genomics and targeted multiplexed proteomics to reveal a clonal population of phenotypically heterogeneous cells. There was a lack of concordance between CTCs and cfDNA of the CSF in the copy number alteration profiles. In an extracellular vesicle surface marker analysis of the CSF, there was a high signal among tetraspanin CD9/CD63/CD81, with CD81 signal the highest across all 3 patients. The data indicates that the CSF may be used as a diagnostic or potentially prognostic tool to measure and characterize disease burden. Citation Format: Stephanie N. Shishido, Amelia Marvit, Saul Priceman, Jana Portnow, Peter Kuhn. Liquid biopsy of cerebrospinal fluid in breast to brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2296.