Validation of targeted next‐generation sequencing of cell‐free DNA from archival cerebrospinal fluid specimens for the detection of somatic variants in cancer involving the leptomeninges: Cytopathologic and radiographic correlation

Abstract Background Leptomeningeal metastases occur across multiple solid and lymphoid cancers, and patients typically undergo cytopathologic assessment of cerebrospinal fluid (CSF) in this setting. For patients diagnosed with metastatic cancer, the detection of actionable somatic mutations in CSF can provide clinically valuable information for treatment without the need for additional tissue collection. Methods The authors validated a targeted next‐generation sequencing assay for the detection of somatic variants in cancer (OncoPanel) on cell‐free DNA (cfDNA) isolated from archival CSF specimens in a cohort of 25 patients who had undergone molecular testing of a prior tumor specimen. Results CSF storage time and volume had no impact on cfDNA concentration or mean target coverage of the assay. Previously identified somatic variants in CSF cfDNA were detected in 88%, 50%, and 27% of specimens diagnosed cytologically as positive, suspicious/atypical, and negative for malignancy, respectively. Somatic variants were identified in 81% of CSF specimens from patients who had leptomeningeal enhancement on magnetic resonance imaging compared with 31% from patients without such enhancement. Conclusions These data highlight the stability of cfDNA in CSF, which allows for cytopathologic evaluation before triage for next‐generation sequencing assays. For a subset of cases in which clinical suspicion is high but cytologic or radiographic studies are inconclusive, the detection of pathogenic somatic variants in CSF cfDNA may aid in the diagnosis of leptomeningeal metastases.