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BRAF mutation is associated with DNA methylation in serrated polyps and cancers of the colorectum
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  1. T Kambara1,*,
  2. L A Simms2,*,
  3. V L J Whitehall2,
  4. K J Spring2,
  5. C V A Wynter2,
  6. M D Walsh2,
  7. M A Barker2,
  8. S Arnold2,
  9. A McGivern2,
  10. N Matsubara3,
  11. N Tanaka3,
  12. T Higuchi4,
  13. J Young2,
  14. J R Jass5,
  15. B A Leggett2
  1. 1Conjoint Gastroenterology Laboratory, Royal Brisbane and Women’s Hospital Research Foundation and Queensland Institute of Medical Research, Brisbane 4029, Australia, and Department of Gastroenterological Surgery, Okayama University Graduate School of Medicine and Dentistry, Okayama 700-8558, Japan
  2. 2Conjoint Gastroenterology Laboratory, Royal Brisbane and Women’s Hospital Research Foundation and Queensland Institute of Medical Research, Brisbane 4029, Australia
  3. 3Department of Gastroenterological Surgery, Okayama University Graduate School of Medicine and Dentistry, Okayama 700-8558, Japan
  4. 4Department of Digestive Surgery, Tokyo Medical and Dental School, Tokyo, Japan, and Department of Pathology, McGill University, Montreal, Quebec, Canada H3A 2B4
  5. 5Department of Pathology, McGill University, Montreal, Quebec, Canada H3A 2B4
  1. Correspondence to:
    Dr B A Leggett
    Conjoint Gastroenterology Laboratory, Royal Brisbane and Women’s Hospital Research Foundation and Queensland Institute of Medical Research, Brisbane 4029, Australia; Barbara_Leggetthealth.qld.gov.au

Abstract

Background and aims: Mutations in BRAF have been linked with colorectal cancers (CRC) showing high level microsatellite instability (MSI-H). However, the distribution of BRAF mutations in MSI-H cancers remains to be clarified with respect to precursor lesions and the CpG island methylator phenotype (CIMP).

Methods: Forty three hyperplastic polyps (HP), nine mixed polyps (MP), five serrated adenomas (SA), 28 conventional adenomas (AD), 18 hereditary non-polyposis colorectal cancers (HNPCC), and 127 sporadic CRC (46 MSI-H and 81 non-MSI-H) were collected from patients undergoing colectomy for either CRC or hyperplastic polyposis. Twenty five of 57 serrated lesions were derived from four patients with hyperplastic polyposis. HP were further subdivided according to recently documented morphological criteria into 27 classical HP and 16 variant lesions described as “sessile serrated adenoma” (SSA). All tumours were screened for BRAF activating mutations.

Results: The BRAF mutation was more frequent in SSA (75%) and MP (89%) than in classical HP (19%), SA (20%), and AD (0%) (p<0.0001), and also in sporadic MSI-H cancers (76%) compared with HNPCC (0%) and sporadic non-MSI-H cancers (9%) (p<0.0001). The BRAF mutation was identified more often in CIMP-high serrated polyps (72%) and CIMP-high CRC (77%) than in CIMP-low (30%) and CIMP-negative (13%) polyps (p = 0.002) as well as CIMP-low (18%) and CIMP-negative (0%) CRC (p<0.0001).

Conclusions: The BRAF mutation was frequently seen in SSA and in sporadic MSI-H CRC, both of which were associated with DNA methylation. Sporadic MSI-H cancers may originate in SSA and not adenomas, and BRAF mutation and DNA methylation are early events in this “serrated” pathway.

  • AD, conventional adenoma (tubular adenoma and tubulovillous adenoma)
  • CIMP, CpG island methylator phenotype
  • CRC, colorectal cancer
  • dHPLC, denaturing high performance liquid chromatography
  • FAP, familial adenomatous polyposis
  • HNPCC, hereditary non-polyposis colorectal cancer
  • HP, hyperplastic polyp
  • MMR, mismatch repair
  • MP, mixed polyp
  • MSI, microsatellite instability
  • MSI-H, high level MSI
  • RFLP, restriction fragment length polymorphism
  • SA, serrated adenoma
  • SSA, sessile serrated adenoma
  • BRAF
  • colorectal cancer
  • serrated pathway
  • CpG island methylator phenotype
  • microsatellite instability
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Footnotes

  • * T Kambara and L A Simms contributed equally to this work.

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