EGFR mutation rate in liquid-based cytology compared with biopsies from primary and metastatic lung cancer using real-time PCR

e19052 Background: Specific EGFR tyrosine kinase inhibitors (TKIs) are recommended as first-line therapy in patients with non-small cell lung cancer (NSCLC) that have active EGFR mutations. Although cytology and tumor biopsy are a very common approaches to evaluate patient eligibility to TKIs, the limited number of tumor cells present in these samples may often constitute a bias for molecular analysis. In this context, the use of sensitive methods to detect EGFR mutations may be of pivotal clinical importance. The aim of this study was two-fold: 1) to determine the accuracy and sensitivity in detecting EGFR mutations between liquid-based cytology (LBC) and bioptic specimens, 2) to compare the performance of direct DNA sequencing and real-time PCR (qPCR) in two different series of cytologic and histologic primary and metastatic NSCLC. Methods: DNA wasextracted from 537 specimens of NSCLC patients including 422 biopsies and 115 ThinPrep (TP) collected samples respectively. EGFR mutations were analyzed by direct sequencing (exons 19 and 21) in 284 biopsies and 68 TP samples and by qPCR (exons 18, 19, 20, 21) in 138 biopsies and 47 LBC samples. Results: The overall specimen insufficiency rate between LBC and biopsies was significantly higher by direct sequencing compared to qPCR (biopsies: 11.6% vs 7.2%) and (LBC: 14.7% vs 2.3%). In the series of 309 valuable cases analyzed by direct sequencing (251 bioptic and 58 LBC), we found 34 (11%) EGFR mutations (11.2% biopsies and 10.3% LBC ). Of interest, a higher percentage of EGFR mutant cases (18.1%) was observed in the 170 valuable cases analyzed by qPCR (11.1% biopsies and 21.4% LBC). Conclusions: Our data indicate that TP collected specimens seem to be more reliable than formalin fixed biopsies for molecular analysis, probably due to the better quality of the extracted DNA. Furthermore, qPCR enabled detection of EGFR mutations in samples with low tumor content for which conventional Sanger sequencing was not informative.