From Discard to Discovery: Leveraging Residual Cytology Fine Needle Aspiration Supernatants for Rapid EGFR and KRAS Mutation Detection in Lung Cancer

INTRODUCTION: Timely molecular testing is essential for guiding targeted therapy in non-small cell lung cancer (NSCLC), yet results are often delayed by limited tissue availability and reliance on formalin-fixed, paraffin-embedded (FFPE) material for next-generation sequencing (NGS). Cytology fine-needle aspiration (FNA) specimens frequently provide the sole diagnostic sample, and their residual supernatants-typically discarded-represent an untapped source of tumor-derived nucleic acids. METHODS: In this pilot study, cytology supernatants from 10 NSCLC cases with known EGFR or KRAS mutations by NGS were analyzed using Idylla™ ctEGFR and ctKRAS Mutation Assays. Each 2-3 mL supernatant sample, stored in CytoLyt® at 4 °C after cell block preparation, was tested without extraction. Idylla™ results were compared with orthogonal NGS data for concordance, and turnaround times for routine FFPE-based testing were evaluated to model potential workflow improvements. RESULTS: All four EGFR-mutated cases (p.L858R, p.G719A, and exon 19 deletions) were correctly detected by Idylla™, yielding 100% concordance with NGS. Among six KRAS-mutated cases, Idylla™ identified all p.G12C variants but missed p.G12V and p.Q61K, achieving 80% overall concordance. Median time from collection to NGS report was 22 days, whereas modeled same-day Idylla™ testing offered a theoretical reduction of approximately 20 days in turnaround time. Discordant cases correlated with relatively low tumor cellularity in cell blocks. CONCLUSIONS: Cytology supernatants preserved in CytoLyt® are a feasible substrate for rapid, cartridge-based molecular testing using the Idylla™ platform. This approach can serve as a complementary or rescue strategy when cellular slide preparations or FFPE tissue is limited or NGS fails, enabling faster access to actionable molecular results in NSCLC.