title: KRAS mutant allele-specific imbalance (MASI) assessment in routine samples of patients with metastatic colorectal cancer.
abstract: OBJECTIVE
  Patients with colorectal cancer harbouring KRAS mutations do not respond to antiepidermal growth factor receptor (anti-EGFR) therapy. Community screening for KRAS mutation selects patients for treatment. When a KRAS mutation is identified by direct sequencing, mutant and wild type alleles are seen on the sequencing electropherograms. KRAS mutant allele-specific imbalance (MASI) occurs when the mutant allele peak is higher than the wild type one. The aims of this study were to verify the rate and tissue distribution of KRAS MASI as well as its clinical relevance.
  
  
  METHODS
  A total of 437 sequencing electropherograms showing KRAS exon 2 mutation was reviewed and in 30 cases next generation sequencing (NGS) was also carried out. Five primary tumours were extensively laser capture microdissected to investigated KRAS MASI tissue spatial distribution. KRAS MASI influence on the overall survival was evaluated in 58 patients. In vitro response to anti-EGFR therapy in relation to different G13D KRAS MASI status was also evaluated.
  
  
  RESULTS
  On the overall, KRAS MASI occurred in 58/436 cases (12.8%), being more frequently associated with G13D mutation (p=0.05) and having a heterogeneous tissue distribution. KRAS MASI detection by Sanger Sequencing and NGS showed 94% (28/30) concordance. The longer overall survival of KRAS MASI negative patients did not reach statistical significance (p=0.08). In cell line model G13D KRAS MASI conferred resistance to cetuximab treatment.
  
  
  CONCLUSIONS
  KRAS MASI is a significant event in colorectal cancer, specifically associated with G13D mutation, and featuring a heterogeneous spatial distribution, that may have a role to predict the response to EGFR inhibitors. The foreseen implementation of NGS in community KRAS testing may help to define KRAS MASI prognostic and predictive significance.
authors.affiliation: Department of Public Health, University of Naples Federico II, Naples, Italy.
authors.forename: Umberto
authors.initials: U
authors.lastname: Malapelle
authors.affiliation: Department of Public Health, University of Naples Federico II, Naples, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Sgariglia
authors.affiliation: Department of Clinical Medicine and Surgery, University of Naples Federico II, Napoles, Italy.
authors.forename: Alfonso
authors.initials: A
authors.lastname: De Stefano
authors.affiliation: Department of Public Health, University of Naples Federico II, Naples, Italy.
authors.forename: Claudio
authors.identifier: http://orcid.org/0000-0002-7479-6457
authors.initials: C
authors.lastname: Bellevicine
authors.affiliation: Department of Public Health, University of Naples Federico II, Naples, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Vigliar
authors.affiliation: Department of Medicine (DIMES)-Anatomic Pathology Unit, Bellaria Hospital, University of Bologna, Bologna, Italy.
authors.forename: Dario
authors.initials: D
authors.lastname: de Biase
authors.affiliation: CNR/IEOS, Institute of Experimental Endocrinology and Oncology, National Research Council, Naples, Italy Department of Molecular Medicine and Medical Biotechnology (DMMBM), University of Naples Federico II, Naples, Italy.
authors.forename: Romina
authors.initials: R
authors.lastname: Sepe
authors.affiliation: CNR/IEOS, Institute of Experimental Endocrinology and Oncology, National Research Council, Naples, Italy Department of Molecular Medicine and Medical Biotechnology (DMMBM), University of Naples Federico II, Naples, Italy.
authors.forename: Pierlorenzo
authors.initials: P
authors.lastname: Pallante
authors.affiliation: Department of Clinical Medicine and Surgery, University of Naples Federico II, Napoles, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Carlomagno
authors.affiliation: Department of Medicine (DIMES)-Anatomic Pathology Unit, Bellaria Hospital, University of Bologna, Bologna, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Tallini
authors.affiliation: Department of Public Health, University of Naples Federico II, Naples, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Troncone
mesh_terms: D022981:Allelic Imbalance; D061067:Antibodies, Monoclonal, Humanized / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000627:therapeutic use; D045744:Cell Line, Tumor; D000068818:Cetuximab; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D004252:DNA Mutational Analysis; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D005091:Exons; D020022:Genetic Predisposition to Disease; D006801:Humans; D007558:Italy; D053208:Kaplan-Meier Estimate; D061346:Laser Capture Microdissection; D009154:Mutation; D009362:Neoplasm Metastasis; D018579:Patient Selection; D010641:Phenotype; D057285:Precision Medicine; D011237:Predictive Value of Tests; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D013997:Time Factors; D014162:Transfection; D016896:Treatment Outcome; D018631:ras Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; C117307:KRAS protein, human; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; C512478:EGFR protein, human; D066246:ErbB Receptors; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D000068818:Cetuximab
keywords: COLON; MOLECULAR BIOLOGY; TUMOUR MARKERS