title: Mutually exclusive FGFR2, HER2, and KRAS gene amplifications in gastric cancer revealed by multicolour FISH.
abstract: Gastric cancer (GC) is a major cause of global cancer mortality. Previous genomic studies have reported that several RTK-RAS pathway components are amplified in GC, with individual tumours often amplifying one component and not others ("mutual exclusivity"). Here, we sought to validate these findings for three RTK/RAS components (FGFR2, HER2, KRAS) using fluorescence in situ hybridisation (FISH) on a series of gastric tumours, cell lines and patient-derived xenografts. Applying dual-colour FISH on 137 gastric tumours (89 FFPE surgical resections and 48 diagnostic biopsies), we observed FGFR2 amplification in 7.3% and HER2 amplification in 2.2% of GCs. GCs exhibiting FGFR2 amplification were associated with high tumour grade (p = 0.034). In FISH positive tumours, striking differences in copy number levels between cancer cells in the same tumour were observed, suggesting intra-tumour heterogeneity. Using a multicolour FISH assay allowing simultaneous detection of FGFR2, HER2, and KRAS amplifications, we confirmed that these components exhibited a mutually exclusive pattern of gene amplification across patients. The FISH data were also strongly correlated with Q-PCR levels and at the protein level by immunohistochemistry. Our data confirm that RTK/RAS components are mutually exclusively amplified in GC, and demonstrate the feasibility of identifying multiple aneuploidies using a single FISH assay. Application of this assay to GC samples, particularly diagnostic biopsies, may facilitate enrollment of GC patients into clinical trials evaluating RTK/RAS directed therapies. However, the presence of intra-tumour heterogeneity may require multiple biopsy samples to be obtained per patient before a definitive diagnosis can be attained.
authors.affiliation: Cancer and Stem Cell Biology, Duke-NUS Graduate Medical School, Singapore. Electronic address: kaks23@yahoo.com.
authors.forename: Kakoli
authors.initials: K
authors.lastname: Das
authors.affiliation: Cancer and Stem Cell Biology, Duke-NUS Graduate Medical School, Singapore.
authors.forename: Bavani
authors.initials: B
authors.lastname: Gunasegaran
authors.affiliation: Department of Medical Oncology, National Cancer Centre Singapore, Singapore; Genome Institute of Singapore, Singapore.
authors.forename: Iain Beehuat
authors.initials: IB
authors.lastname: Tan
authors.affiliation: Cancer and Stem Cell Biology, Duke-NUS Graduate Medical School, Singapore.
authors.forename: Niantao
authors.initials: N
authors.lastname: Deng
authors.affiliation: Department of Pathology, Singapore General Hospital, Singapore.
authors.forename: Kiat Hon
authors.initials: KH
authors.lastname: Lim
authors.affiliation: Cancer and Stem Cell Biology, Duke-NUS Graduate Medical School, Singapore; Genome Institute of Singapore, Singapore; Cancer Science Institute of Singapore, National University of Singapore, Singapore; Cellular and Molecular Research, National Cancer Centre, Singapore. Electronic address: gmstanp@duke-nus.edu.sg.
authors.forename: Patrick
authors.initials: P
authors.lastname: Tan
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor / Q000235:genetics; D005260:Female; D005784:Gene Amplification; D018628:Gene Dosage; D056726:Genetic Association Studies; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*; D051497:Receptor, Fibroblast Growth Factor, Type 2 / Q000235:genetics*; D013274:Stomach Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D018631:ras Proteins / Q000235:genetics*
chemical_list: D014408:Biomarkers, Tumor; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D018719:Erb-b2 Receptor Tyrosine Kinases; D051497:Receptor, Fibroblast Growth Factor, Type 2; D018631:ras Proteins; C117307:KRAS protein, human; C508053:ERBB2 protein, human; C496353:FGFR2 protein, human
keywords: FGFR2; Gastric cancer; Gene amplification; HER2; KRAS; Multicolour FISH