Direct sequencing in cytological specimens as a useful strategy for detecting EGFR mutations in non-small cell lung cancer patients

Abstract

New therapeutics targeting epidermal growth factor receptor (EGFR) have significantly improved tumor responses to therapy in non-small cell lung cancer (NSCLC) patients. Molecular testing for EGFR mutations informs important therapeutic decisions in clinical practice. In this study, we sought to validate the clinical relevance of sequencing-based EGFR mutation testing combined with cytological analysis using body fluid specimens. Two NSCLC cell lines were used in sensitivity analyses. In addition, we performed cytological analyses and directly sequencing of exons 18-21, for 32 specimens. The absence of EGFR mutations determined by direct sequencing in 14 specimens was confirmed by real-time PCR. Changes made to patients' therapeutic strategies after reports of EGFR mutation status were investigated by querying electronic medical records. Sensitivity studies showed that detection of in-frame deletions in exon 19 and point mutations in exon 21 was possible in specimens containing 10% and 5% mutant DNA, respectively. In clinical practice, EGFR mutations were detected in 18 of 32 specimens (56.3%). Twelve patients with EGFR mutations detected by direct sequencing were started on treatment with EGFR tyrosine kinase inhibitor (TKI) after reports of EGFR mutation. EGFR-TKI therapy was discontinued for two patients with TKI-resistant T790M mutation. The results of real-time PCR were consistent with those of direct sequencing in 13 of 14 specimens (92.9%) in which no mutation was detected by direct sequencing. Combined direct sequencing and cytological analysis of body fluid specimen might be clinically useful and sensitive test for the detection of EGFR mutations in NSCLC patients.