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WHO Classification of Tumours
Adenoma, NOS
Colon and rectum


Definition

A non-invasice, benign neoplasm arising from the epithelium. It may be encapsulated or non-encapsulated. The neoplastic epithelial cells may or may not display moderate cellular atypia or dysplasia. Representative examples are pituitary gland adenoma, follicular adenoma of the thyroid gland, and adenomas (or adenomatous polyps) of the gastrointestinal tract.

Adenomas of the colon and rectum
Adenomas are defined by the presence of dysplastic epithelium. This is characterized histopathologically by enlarged, hyperchromatic nuclei, varying degrees of nuclear spindling and stratification, and loss of polarity. Dysplasia can be low-grade or high-grade, depending on the degree of architectural complexity, extent of nuclear stratification, and severity of abnormal nuclear morphology. Foci in invasive growth can be encountered in an adenoma with high-grade dysplasia. For such lesions, the terms high-grade dysplasia as well as intramucosal carcinomas are used. Paneth cells, neuroendocrine cells and squamous cell aggregates may be seen in adenomas

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Bansal M, Fenoglio CM, Robboy SJ, King DW (1984)
Are metaplasias in colorectal adenomas truly metaplasias?
Am J Pathol 115: 253-65




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Iwashita A, Watanabe H, Enjoji M (1989)
Argyrophil and argentaffin cells in adenomas of the colon and rectum.
Fukuoka Igaku Zasshi 80: 114-24




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Wada R (2009)
Proposal of a new hypothesis on the development of colorectal epithelial neoplasia: nonspecific inflammation--colorectal Paneth cell metaplasia--colorectal epithelial neoplasia.
Digestion 79 Suppl 1: 9-12



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Macroscopically, most adenomas are polypoid with protrusion into the colorectal lumen, either sessile with broad attachment or on a stalk. A smaller number are flat or depressed

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Lambert R, Kudo SE, Vieth M, Allen JI, Fujii H, Fujii T, Kashida H, Matsuda T, Mori M, Saito H, Shimoda T, Tanaka S, Watanabe H, Sung JJ, Feld AD, Inadomi JM, O'Brien MJ, Lieberman DA, Ransohoff DF, Soetikno RM, Zauber A, Teixeira CR, Rey JF, Jaramillo E, Rubio CA, Van Gossum A, Jung M, Jass JR, Triadafilopoulos G (2009)
Pragmatic classification of superficial neoplastic colorectal lesions.
Gastrointest Endosc 70: 1182-99




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Park DH, Kim HS, Kim WH, Kim TI, Kim YH, Park DI, Kim HJ, Yang SK, Byeon JS, Lee MS, Chung IK, Jung SA, Jeen YT, Choi JH, Choi H, Han DS (2008)
Clinicopathologic characteristics and malignant potential of colorectal flat neoplasia compared with that of polypoid neoplasia.
Dis Colon Rectum 51: 43-9; discussion 49



and often recognizable macroscopically by mucosal reddening, subtle changes in texture, or highlighting by specialized endoscopic techniques.

Most adenomas are < 1 cm in size and have tubular architecture. Some have a villous or tubulovillous architecture. Unusual histopathological patterns such as microtubular adenoma occur.

The characteristics of adenomas are associated with the occurrence of synchronous and metachronous carcinoma. Adenomas of larger size (1 cm), more extensive villous architecture, and high-grade intraepithelial neoplasia/dysplasia, termed “advanced adenomas”

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Heitman SJ, Ronksley PE, Hilsden RJ, Manns BJ, Rostom A, Hemmelgarn BR (2009)
Prevalence of adenomas and colorectal cancer in average risk individuals: a systematic review and meta-analysis.
Clin Gastroenterol Hepatol 7: 1272-8



, and flat depressed adenomas
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Lambert R, Kudo SE, Vieth M, Allen JI, Fujii H, Fujii T, Kashida H, Matsuda T, Mori M, Saito H, Shimoda T, Tanaka S, Watanabe H, Sung JJ, Feld AD, Inadomi JM, O'Brien MJ, Lieberman DA, Ransohoff DF, Soetikno RM, Zauber A, Teixeira CR, Rey JF, Jaramillo E, Rubio CA, Van Gossum A, Jung M, Jass JR, Triadafilopoulos G (2009)
Pragmatic classification of superficial neoplastic colorectal lesions.
Gastrointest Endosc 70: 1182-99



have a higher frequency of malignancy, although depressed adenomas have a lower frequency of KRAS mutation than do polypoid adenomas
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Morita T, Tomita N, Ohue M, Sekimoto M, Yamamoto H, Ohnishi T, Tada M, Ikenaga M, Miyake Y, Sakita I, Tamaki Y, Matsuura N, Ito M, Monden M (2002)
Molecular analysis of diminutive, flat, depressed colorectal lesions: are they precursors of polypoid adenoma or early stage carcinoma?
Gastrointest Endosc 56: 663-71



. Patients who have an adenoma of 20 mm or more with tubulovillous or villous architecture in a proximal location in the colon, multiplicity of adenomas (five or more) or are male have more frequent development of a metachronous advanced adenoma or carcinoma
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Martínez ME, Baron JA, Lieberman DA, Schatzkin A, Lanza E, Winawer SJ, Zauber AG, Jiang R, Ahnen DJ, Bond JH, Church TR, Robertson DJ, Smith-Warner SA, Jacobs ET, Alberts DS, Greenberg ER (2009)
A pooled analysis of advanced colorectal neoplasia diagnoses after colonoscopic polypectomy.
Gastroenterology 136: 832-41



. The clinical implications of serration in adenomas and of sessile serrated adenomas/polyps are not yet well-defined
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Bosman FT, Carneiro F, Hruban RH, Theise ND (Eds.)
WHO Classification of Tumours of the Digestive System.
4th Edition
International Agency for Research on Cancer: Lyon 2010



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> Histological subtypes
Tubular adenoma
Villous adenoma
Tubulovillous adenoma


Frequency of colorectal adenocarcinoma in adenomas relative to size and architecture
Frequency of colorectal adenocarcinoma in adenomas relative to size and architecture