Detection of actionable oncogene drivers alterations in HER2-amplified gastric cancer by next generation sequencing.

Abstract

67 Background: HER2 amplified cases are the only subset of gastric carcinoma (GC) patients with an approved targeted therapy (≈20%). In GC it is still unknown if there is a mutually exclusive pattern of mutations in major driver oncogenes. We performed a systematic search for targetable oncogenes in a cohort of HER2 amplified GC patients. Methods: 53 Formalin-fixed paraffin embedded samples from HER2 amplified GC patients (43 tumor and 10 normal samples) were selected for next generation sequencing (NGS). Before DNA extraction a macrodissection procedure was performed to guarantee at least 30% tumor in all cases. DNA samples were sequenced using the Ion Torrent Personal Genome Machine (PGM) sequencing platform (Life Technologies, Carlsbad, CA, USA). The Ion AmpliSeq Cancer Hotspot Panel v2 was used. This panel encompasses more than 2800 mutational hotspots of 50 oncogenes and tumor suppressor genes. Data were processed using the Ion Torrent platform-specific pipeline software Torrent suite v4.2. Moreover, sequencing data were analyzed with Ion Reporter software 4.2 to detect any copy number alteration of the genes included in the panel. Results: We successfully sequenced all samples. We identified 89 mutations in 12 genes (range from 1 ~ 9). The most frequent significant mutations included TP53 mutations (30), PI3KCA (3), SMAD4 (3), CDKN2A (4), CTNNB1 (3) and MET (3). Other mutations were found in KRAS, NOTCH, APC, and VHL genes. We also detected potential amplifications in the KRAS (4), EGFR (9), PI3KCA (11), AKT (6), FGFR (6), CDKN2A (4) and CDH1(8) genes. Among 43 tumor specimens, 86% of specimens harbored at least one genetic alteration, most of them linked to actionable mutations or amplifications Conclusions: Within HER2 amplified GCs, there are additional subsets with a potentially targetable oncogene. Future testing for these targets will benefit from including HER2 amplified GC patients Supported by the Spanish Ministry of Health, Fondo de Investigaciones Sanitarias grant PI11/01005 and European FEDER (PN I+D+I 2008‐20011).