serrated colorectal polyp; serrated adenoma

Introduction

• distinct from adenomas (adenomatous polyps)

Classification

• includes
  • sessile serrated adenomas
    • sessile or flat
    • distributed toward the proximal colon
    • endoscopically subtle
    • some share molecular features with a group of colon cancers that account for many cancers that develop after colonoscopy
      • the BRAF mutation
      • the CpG island methylator phenotype
      • microsatellite instability
  • traditional serrated adenomas
    • infrequent, dysplastic, often protuberant or pedunculated, located toward the distal colon

Etiology

• serrated polyposis syndrome

Pathology

• large serrated polyps may be associated with colorectal cancer
  • associated with DNA mismatch repair deficiency & microsatellite instability
  • associated with BRAF mutations (78%) or K-ras mutations (11%)
  • benign hyperplastic polyps tend to have more K-ras mutations than BRAF mutations
  • MLH1 promoter methylation is frequent
  • associated with smoking & estrogen withdrawal
  • these colon cancers tend to occur on the right side of the colon
• no increased risk of proximal colon cancer with distal (rectosigmoid) hyperplastic polyps

* pathologic distinction between hyperplastic polyps sessile serrated adenomas is not reliable in clinical practice & can be difficult, even for experts

Management

• follow-up colonoscopy in 3 years for
  • serrated polyps >= 10 mm
  • dysplastic serrated polyps
  • traditional serrated adenomas
• follow-up colonoscopy in 5 years for
  • serrated polyps < 10 mm
• see notes

Notes

• pathologic distinction between hyperplastic polyps sessile serrated adenomas is not reliable in clinical practice & can be difficult, even for experts

More general terms

• colorectal polyp

Additional terms

• serrated polyposis syndrome; hyperplastic polyposis syndrome