Survival benefit of gefitinib treated non-small-cell lung cancer patients with exon 19 deletion mutations in epidermal growth factor receptor (EGFR), detected by a new sensitive PCR-based method

Abstract

10614 Background: As for two common types of EGFR mutations, patients with exon 19 deletion mutations have longer survival than those with the L858R point mutations in exon 21 after treatment with EGFR inhibitors. We have developed a simple, polymerase chain reaction (PCR)-based method to detect exon 19 deletion mutations, and evaluated survival benefit of gefitinib treated patients with exon 19 deletion mutations versus patients without these mutations. Patients and methods: Tumor tissue was microdissected under stereoscopic microscopy from formalin-fixed paraffin-embedded sections, and DNA was extracted from tumor cells with DNeasy (Qiagen). Our method consisted of two different semi-nested PCRs with the deletion screening PCR and the common deletion specific PCR. All of the known deletions present in cell lines were detected by this method without direct sequencing. The result was validated by sequencing of exon 19. 73 non-small-cell lung cancer (NSCLC) Japanese patients treated with gefitinib were analyzed with this method. Study group consisted of 28 females (38%), 29 never smokers (40%) and 57 patients with adenocarcinoma (78%). Results: The PCR-based method detected mutations at mutant to wild type DNA copy ratio of 1/600, and in samples as small as 30 ng of purified DNA. Exon 19 deletion mutations were found in 25 (34%) patients. This method was more sensitive than conventional sequencing. The sequencing was performed in 19 patients with mutations and could not detect 3 deletions. Among 60 assessable patients 14 had overall response (23%). Objective response rates to gefitinib were observed in 7/21 patients with exon 19 deletion mutations (33%), and 7/39 patients without exon 19 deletion mutations (17%) (P = .211). Patients with exon 19 deletion mutations survived significantly longer than those without exon 19 deletion mutations (P = .017). Conclusions: The PCR-based method to detect exon 19 deletion mutations is cost effective and very sensitive, compared to previously described methods. We demonstrated survival benefit in NSCLC patients with exon 19 deletion mutations treated with gefitinib, and our PCR-based method is easily applicable for clinical use. No significant financial relationships to disclose.