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Colon tumor

Polyps

Adenoma-general of colon


Reviewers: Shilpa Jain, M.D, New York University (see Reviewers page)
Revised: 19 October 2010, last major update September 2010
Copyright: (c) 2003-2010, PathologyOutlines.com, Inc.

Definition / General
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● Well established premalignant lesion, usually with polypoid areas of epithelial dysplasia
● “Adenoma” is an incorrect term - they are not benign neoplasms

Epidemiology
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● In U.S., present in colon in 20% at age 40 years, 50% at age 60 years
● In U.S. autopsy studies, almost all have tubular adenomas, <5% have tubulovillous or villous adenomas
● Low incidence in developing countries
● No gender predilection
● Decreased risk of adenoma is associated with dietary fiber intake (Lancet 2003;361:1491), fruit consumption in women (Cancer Res 2006;66:3942), folate intake (J Nutr 2005;135:2468)
● Only weak association between fiber and adenoma recurrence (Am J Gastroenterol 2005;100:2789)

Clinical
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● Slow growing
● 30% develop new polyps after mean 26 month follow up; higher risk if 3 or more adenomas and at least one in proximal colon (Dis Colon Rectum 2004;47:323)
● Risk of invasive colorectal adenocarcinoma in the adenoma depends on size: <1% if < 1 cm vs. 10% if > 2 cm; higher risk if villous component
● Risk of subsequent carcinoma is related to 3 or more polyps, polyp location at transverse colon or proximal, or [one study] presence of monotonous population of elongated cells (Am J Surg Pathol 2006;30:1120)

● “Advanced adenomas” receive more aggressive clinical management (i.e. repeat colonscopy in 3 years instead of 5 years), and includes:
● >3 adenomas
● Any adenoma >1 cm with villous architexture
● Any adenoma with high grade dysplasia

Treatment
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● Excision of a pedunculated adenoma, even with invasive carcinoma, is considered adequate treatment if margin is negative, there is no vascular or lymphatic invasion and carcinoma is moderate or well differentiated
● Invasive adenocarcinoma in a sessile polyp requires more than polypectomy

Gross
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● Classified as pedunculated (with stalk), sessile or flat
● Tubular are red (darker than surrounding mucosa)
● Villous are shaggy with papillary fronds
● True margin of resection should be inked when grossing, or can be determined by diathermy artifact

Gross images
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Micro
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● Either conventional (tubular, tubulovillous [5%] or villous [1%]), serrated or flat adenomas
● Villous: At least >75% villous component
● Tubulovillous: 25-75% of villous component
● Tubular: less than 25% of villous component
● The degree of villous differentiation increases with size of the adenoma

● All subtypes contain epithelial proliferative dysplasia
● Dysplasia can be classified as low grade or high grade, although some GI pathologists recommend not using high grade dysplasia terminology unless clinicians want to know
Low grade: pseudostratification or stratification of nuclei that reach only luminal half of the cell, but don’t reach cell surface; apical mucin is present; nuclei are elongated and dysplastic; mitotic activity, atypical mitosis and loss of polarity are minimal
High grade: Cytological and architectural changes of dysplasia; nuclei are enlarged, hyperchromatic or vesicular with prominent nucleoli; nuclei are stratified and reach luminal border; architectural changes include back to back glands, cribriform glands or irregular budding/branching of crypts; mitotic figures are prominent; reduced mucin; necrosis may be present
● Note: high grade dysplasia present in 12% of adenomas
● By definition, no invasion through muscularis mucosa into submucosa
Intramucosal carcinoma: invasion of mucosa or muscularis mucosa (but not beyond) with desmoplastic response; no biologic potential for metastases

Additional references
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Am J Gastroenterol 2006;101:255 (prevalence)

End of Colon tumor > Polyps > Adenoma-general of colon


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