P2.03-019 Sizing Capillary Electrophoresis with PCR to Detect Various EGFR Exon 19 Deletions in Non-Small Cell Lung Cancer

This study points out an issue of PCR-based methods to detect exon 19 deletions. PCR methods are used for clinical examination, because they are useful, rapid and cost-effective to detect EGFR mutations. Exon 19 deletions are most important among EGFR mutations to dictate EGFR tyrosine kinase inhibitors (EGFR-TKIs) therapy in non-small cell lung cancer (NSCLC), and have various species. The sensitive PCR methods select major exon 19 deletions, but cannot detect unusual variants. We investigated the clinical significance of minority exon 19 deletions. A series of 73 NSCLC patients, which were treated with EGFR-TKI for recurrent disease after they had undergone surgery from 1992 to 2004. In all cases, Microdissection and direct sequence were performed. Scorpion Amplification Refractory Mutation System (ARMS) and cobas version 2.0, as sensitive PCR methods, were performed in 47 patients along with sizing capillary electrophoresis for the exhaustive detection of exon 19 deletions. EGFR mutations were detected from 35 patients (47.9%), which were one exon 18 mutation, 23 exon 19 deletions, and 11 exon 21 mutations in all 73 cases. The catalog of somatic mutation in cancer (COSMIC) database included 174 different exon 19 deletions in 4190 submitted cases at December 2014. E746_A750 deletion was most common deletion of exon 19, accounting for 70% of the total exon 19 deletions (2931/4190). Predicted frequency of exon 19 tested by Scorpion-ARMS was 81.6% (3419/4190), and that of cobas version 2.0 had 82.5% (3457/4190) in the detection of various exon 19 deletions. In clinical samples of this study, Scorpion-ARMS and cobas version 2.0 failed to detect four exon 19 deletions, in two squamous cell carcinomas (EGFR-TKI effects were stable disease and no assessable patient) and two papillary adenocarcinomas (EGFR-TKI effects were stable disease and no assessable patient). One of papillary adenocarcinoma had minority deletion ‘T751_I759 deletion and insertion S’, which had long stable disease for 43.4 months in EGFR-TKI therapy. Sizing capillary electrophoresis was able to detect this deletion. This study suggests sizing capillary electrophoresis is necessary for the exhaustive detection of exon 19 deletions, and may identify tumors responsive to EGFR-TKIs therapy, especially those with unusual deletions.