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BRAF mutation and gene methylation frequencies of colorectal tumours with microsatellite instability increase markedly with patient age
  1. B Iacopetta1,
  2. W Q Li1,
  3. F Grieu1,
  4. A Ruszkiewicz2,
  5. K Kawakami3
  1. 1School of Surgery and Pathology, University of Western Australia, Western Australia, Australia
  2. 2Division of Tissue Pathology, Institute of Medical and Veterinary Science, Adelaide, South Australia, Australia
  3. 3Department of Surgery, Kanazawa University School of Medicine, Ishikawa, Japan
  1. Correspondence to:
    Dr B Iacopetta
    School of Surgery and Pathology M507, 35 Stirling Hwy, Nedlands 6009, Australia; bjiac{at}meddent.uwa.edu.au

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The microsatellite instability phenotype (MSI+) is observed in approximately 25% of colon cancers and 2% of rectal cancers. MSI+ is a hallmark of almost all hereditary non-polyposis colorectal cancers (HNPCC) where it is associated with germline mutations in one of the DNA mismatch repair genes.1 However, the large majority of MSI+ cancers occur as sporadic cases that arise following methylation induced silencing of the hMLH1 gene promoter. Sporadic MSI+ tumours are believed to originate in serrated polyps and display frequent and concurrent methylation of gene promoter regions but low frequencies of KRAS and TP53 mutations.2 In contrast, HNPCC associated MSI+ tumours originate in conventional adenomas and show frequent APC and KRAS mutations but infrequent methylation. Another striking difference is that BRAF mutations occur in most …

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