Is the Idylla EGFRMutation Assay feasible on archival stained cytological smears? A pilot study

AimThe rapid and fully automated Idylla EGFRMutation Assay has been specifically designed to process formalin-fixed, paraffin-embedded sections without requiring preliminary DNA extraction. This study evaluates whether this approach can also process archival smears from patients with non–small cell lung cancer (NSCLC) by scraping the stained cellular material directly into the cartridge.MethodsThe study was divided into two parts. In the first part, we carried out Idylla EGFRMutation Assay on archival stained smears from 39 patients with NSCLC. Among these, 14 cases harboured a mutation in either exon 19 (n=11) or exon 21 (n=3), previously detected on DNA extracts by fragment length and TaqMan assays. In the second part, we evaluated whether de-staining of the smears could reduce background fluorescence.ResultsThe Idylla EGFRMutation Assay confirmed the presence of EGFRmutation in 11 instances (78.6%). However, concordance was higher for exon 19 deletions (10/11) than for exon 21 p.L858R assessments. Raw data showed a high background fluorescence in channel 2, where the EGFRexon 21 p.L858R mutation was detected. This interference, due to dye residues from the original staining, was partially reduced by de-staining the cytological material.ConclusionsOur data, although preliminary, show that the Idylla EGFRMutation Assay can reliably process most archival smears without requiring preliminary DNA extraction. Results may be further improved by de-staining the cellular material before insertion into the cartridge.