title: Low percentage of KRAS mutations revealed by locked nucleic acid polymerase chain reaction: implications for treatment of metastatic colorectal cancer.
abstract: Metastatic colorectal cancer (mCRC) is frequently characterized by the presence of mutations of the KRAS oncogene, which are generally associated with a poor response to treatment with anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibodies. With the methods currently used, a case is classified as KRAS-mutated when approximately 20% of the cells bear an activating KRAS mutation. These considerations raise the question of whether cells with a mutated KRAS can be found in mCRC cases classified as KRAS wild-type when more sensitive methods are used. In addition, the issue arises of whether these mCRC cases with low proportion of KRAS-mutated cells could account at least in part for the therapeutic failure of anti-EGFR therapies that occur in 40-60% of cases classified as KRAS wild type. In this study, we compared the classical assays with a very sensitive test, a locked nucleic acid (LNA) polymerase chain reaction (PCR), capable of detecting KRAS-mutated alleles at extremely low frequency (detection sensitivity limit 0.25% mutated DNA/wild-type DNA). By analyzing a cohort of 213 mCRC patients for KRAS mutations, we found a 20.6% discordance between the sequencing/TheraScreen methods and the LNA-PCR. Indeed, 44 mCRC patients initially considered KRAS wild type were reclassified as KRAS mutated by using the LNA-PCR test. These patients were more numerous among individuals displaying a clinical failure to anti-EGFR therapies. Failure to respond to these biological treatments occurred even in the absence of mutations in other EGFR pathway components such as BRAF.
authors.affiliation: Molecular Diagnostic Division, Istituto di Ricovero e Cura a Carattere Scientitifico Azienda Ospedaliera Universitaria San Martino, Genova, Italy.
authors.forename: Mariella
authors.initials: M
authors.lastname: Dono
authors.forename: Carlotta
authors.initials: C
authors.lastname: Massucco
authors.forename: Silvana
authors.initials: S
authors.lastname: Chiara
authors.forename: Claudia
authors.initials: C
authors.lastname: Sonaglio
authors.forename: Marco
authors.initials: M
authors.lastname: Mora
authors.forename: Anna
authors.initials: A
authors.lastname: Truini
authors.forename: Giannamaria
authors.initials: G
authors.lastname: Cerruti
authors.forename: Gabriele
authors.initials: G
authors.lastname: Zoppoli
authors.forename: Alberto
authors.initials: A
authors.lastname: Ballestrero
authors.forename: Mauro
authors.initials: M
authors.lastname: Truini
authors.forename: Manlio
authors.initials: M
authors.lastname: Ferrarini
authors.forename: Simona
authors.initials: S
authors.lastname: Zupo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D001483:Base Sequence; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D004252:DNA Mutational Analysis; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000276:immunology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D009362:Neoplasm Metastasis; D009841:Oligonucleotides; D016133:Polymerase Chain Reaction / Q000379:methods*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins / Q000235:genetics*
chemical_list: D000911:Antibodies, Monoclonal; C117307:KRAS protein, human; D009841:Oligonucleotides; D011518:Proto-Oncogene Proteins; C477371:locked nucleic acid; D066246:ErbB Receptors; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins