Colon

• Neoplastic colon polyp with at least low grade dysplasia
• Precursor to invasive adenocarcinoma

• Dysplastic nuclei (elongated and hyperchromatic pseudostratification)
• < 25% villous component

• The word adenoma should not be used on its own, to avoid confusion with sessile serrated adenoma and traditional serrated adenoma
• > 25% villous component indicates tubulovillous adenoma or villous adenoma

• ICD-10: K63.5 - colon polyp
• ICD-10: D12.6 - adenomatous polyp

• Incidence increases with age; commonly encountered in patients over 50
• Estimated that 25% of men and 15% of women undergoing colonoscopy are found to have at least 1 adenoma (N Engl J Med 2006;355:2551)
• Men more commonly affected than women (Gastrointest Endosc 2011;74:135)

• Found more commonly in the left colon and rectum compared with other polyps

• Has a well documented adenoma to carcinoma sequence that involves mutations in KRAS, TP53, APC and beta catenin (Cell 1990;61:759)
• Activation of KRAS leads to downstream signaling that influences survival, antiapoptosis and proliferation (J Gastroenterol Hepatol 2012;27:1423)
• Wnt pathway: activation of Wnt pathway leads to beta catenin accumulation in the nucleus and subsequent transcription and cell proliferation
• Mutations include loss of function of APC or beta catenin mutations that resist degradation by APC (J Gastroenterol Hepatol 2012;27:1423)

• Decreased risk of conventional colorectal adenomas is associated with
  • Increased dietary fiber intake (Lancet 2003;361:1491)
  • Fruit consumption in women (Cancer Res 2006;66:3942)
  • Folate intake (J Nutr 2005;135:2468)

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• < 1 cm: usually asymptomatic and detected by screening colonoscopy
• > 1 cm: may bleed, lead to iron deficiency anemia, obstruction; increased risk of progressing to carcinoma
• Mostly left sided in spontaneous polyps and in familial adenomatous polyposis; right sided in Lynch syndrome (Gut 2002;50:382)

• Diagnosis is made by histologic confirmation

• Colonoscopy is diagnostic and potentially curative (via polypectomy)
• High grade dysplasia and large polyps may warrant endoscopic mucosal resection or partial colectomy

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Contributed by Laleh Montaser, M.D.


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Contributed by Andrew L.J. Dunn, M.D. and Christopher Hartley, M.D.


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• Inflammatory polyp:
  • Nuclei can become elongated like a tubular adenoma but nuclei are typically vesicular with round borders
• Tubulovillous adenoma, villous adenoma:
  • Surface architecture has > 25% villous component

• J Clin Pathol 2018;71:7, Int J Oncol 2013;43:973, Cell 2009;137:623

Which of the following gene mutations is implicated in a majority of tubular adenomas?

1. ALK
2. BAP1
3. KRAS
4. MDM2

C. KRAS mutations are implicated in up to 60% of adenomas and adenocarcinomas. BAP1 mutations are present in a subset of melanocytic tumors and mesotheliomas. MDM2 is amplified in liposarcoma and some of its variants. ALK mutations can be seen in inflammatory myofibroblastic tumor, anaplastic large cell lymphoma and a subset of lung adenocarcinomas.

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Reference: Tubular adenoma