title: KRAS mutations in microsatellite instable gastric tumours: impact of targeted treatment and intratumoural heterogeneity.
abstract: In gastric cancer (GC), epidermal growth factor receptor (EGFR) overexpression associates with poor prognosis. Addition of a chimeric monoclonal antibody against EGFR (cetuximab) to first-line treatment of metastatic colorectal tumours improved outcomes of patients (stratified for KRAS wild-type cancers), whereas GC patients did not benefit from this approach. In GC, however, stratification based on KRAS mutations was not performed, and the 30 % KRAS mutation frequency in microsatellite instable cancers (MSI), which represents ∼4 % of total GC, was disregarded. Further, intratumoural heterogeneity regarding KRAS mutant subpopulations might also contribute to anti-EGFR therapy failure. We assessed the mutational status of the entire KRAS coding sequence in 19 MSI-GC cases by multiplex PCR/sequencing and used peak height ratio determined from electropherograms from KRAS heterozygous mutants and histopathological evaluation to infer tumour heterogeneity in GC. Using 2 multiplex reactions per sample, we found that 26 % (5/19) of MSI-GC cases harboured KRAS mutations (2 G12D, 2 G13D, 1 G12V). No mutations were found outside the codon 12 and 13 hotspots. Our analysis supported the co-existence of KRAS-positive and KRAS-negative tumour populations in 4/5 MSI-GC cases. In conclusion, the method developed stands as a cost-effective and practical way for mutation screening of the entire KRAS coding sequence. KRAS mutations are frequent in our series of MSI cases and are often found in a subpopulation of the tumour and not in the whole tumour. Further studies are needed to access the implications of this heterogeneity in KRAS mutant and wild-type tumour clones in anti-EGFR therapy response.
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal.|Faculty of Medicine, University of Porto, Porto, Portugal.
authors: Pedro
authors: P
authors: Queirós
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal.
authors: Hugo
authors: H
authors: Pinheiro
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal.
authors: Joana
authors: J
authors: Carvalho
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal.
authors: Patrícia
authors: P
authors: Oliveira
authors: Department of Pathology, Centro Hospitalar S. João, Porto, Portugal.
authors: Irene
authors: I
authors: Gullo
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal.|Faculty of Medicine, University of Porto, Porto, Portugal.|Department of Pathology, Centro Hospitalar S. João, Porto, Portugal.
authors: Fátima
authors: F
authors: Carneiro
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal.
authors: Gabriela M
authors: GM
authors: Almeida
authors: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal. carlaol@ipatimup.pt.|IPATIMUP, Institute of Molecular Pathology and Immunology of the University of Porto, Porto, Portugal. carlaol@ipatimup.pt.|Faculty of Medicine, University of Porto, Porto, Portugal. carlaol@ipatimup.pt.
authors: Carla
authors: http://orcid.org/0000-0001-8340-2264
authors: C
authors: Oliveira
mesh_terms: D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D006801:Humans; D053842:Microsatellite Instability; D060885:Multiplex Polymerase Chain Reaction; D009154:Mutation; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D013274:Stomach Neoplasms / Q000188:drug therapy / Q000235:genetics*; D018631:ras Proteins / Q000235:genetics*
chemical_list: C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D066246:ErbB Receptors; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
keywords: Gastric cancer; Gastric cancer treatment; KRAS; MSI; Microsatellite instability