Utility of Cerebrospinal Fluid Cell-Free DNA in Patients with EGFR-Mutant Non-Small-Cell Lung Cancer with Leptomeningeal Metastasis

Background: Leptomeningeal metastasis (LM) is a fatal complication of advanced non-small-cell lung cancer (NSCLC). Objective: The aim of this study was to evaluate the utility of cerebrospinal fluid (CSF) as a medium for epidermal growth factor receptor (EGFR) mutation testing in clinical practice. Patients and methods: We prospectively enrolled patients with EGFR-mutant NSCLC who underwent CSF sampling for suspected LM. The supernatant of CSF after routine cytology examination was collected. The diagnosis of LM was established according to EANO-ESMO criteria. CSF and plasma cell-free DNA (cfDNA) were retrieved for EGFR mutation testing. Results: Fifty-one patients with a median age of 62.7 years were enrolled. The median duration from initial diagnosis to CSF sampling was 23.0 months and most patients (94.1%) had received at least one EGFR-tyrosine kinase inhibitor. Adenocarcinoma cells were found in 37 CSF samples (72.5%), and 48 (94.1%) patients had confirmed or probable LM. Thirty-five of these 48 patients (72.9%) had valid EGFR mutation-testing results using CSF cfDNA and tended to have higher white blood cell counts and positive cytology in their CSF compared to those with invalid mutation testing results. The overall detection rate of EGFR mutation in CSF cfDNA was 68.8%, and the T790M detection rate was 14.6%. In 37 patients with paired CSF and plasma samples, the concordance rate of the EGFR mutation results was 29.7%. Conclusions: For patients with EGFR-mutant NSCLC with LM, CSF supernatant is a valuable source for EGFR mutation testing and may provide important information.