Diagnosis of leptomeningeal metastasis through identification of circulating tumor cells in cerebrospinal fluid using the TargetSelector™ assay

Abstract Introduction: Diagnosis of leptomeningeal metastasis (LM) is limited by low sensitivity of cerebrospinal fluid (CSF) cytopathology. Detecting circulating tumor cells (CTCs) in CSF might be more sensitive. We evaluated if TargetSelector™ (TS), a novel assay that captures CTCs in peripheral blood, detects CTCs in CSF.Methods: We enrolled adults with metastatic solid tumors or primary CNS malignancies and clinical suspicion for LM to undergo lumbar puncture (LP) for CSF cytopathology and TS. TS captured CTCs using a primary 10-antibody mixture, streptavidin-coated microfluidic channel, and biotinylated secondary antibodies. CTCs from patients with metastatic breast cancer (MBC) were assessed for estrogen receptor (ER) expression by fluorescent antibody and HER2 amplification by fluorescent in situ hybridization (FISH). CSF cell-free DNA (cfDNA) was extracted for next-generation sequencing (NGS). Results: Fourteen patients, median age 56 years (range, 32-75), underwent diagnostic LP. Primary malignancies were breast (n=10), lung (n=1), colon (n=1), CNS lymphoma (n=1), and glioma (n=1). Among thirteen patients who underwent CSF evaluation by TS, TS had sensitivity of 83% (95% Confidence Interval [CI], 33-100%) and specificity of 86% (95% CI, 42-100%) for LM, defined as positive CSF cytology and/or unequivocal MRI findings. Among MBC patients, concordance of ER and HER2 status between CTCs and metastatic biopsy were 60% and 75%, respectively. NGS of CSF cfDNA identified somatic mutations in three MBC patients, including one with PIK3CAp.H1047L in blood and CSF.Conclusions: TargetSelector™ is a viable platform to detect CSF CTCs, with potential use as a diagnostic tool for LM. Additional, larger studies are warranted.