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WHO Classification of Tumours
Adenoma, NOS
Appendix


Definition

A non-invasive, 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.

Appendiceal adenomas are defined as lesions that are confined to the appendix with no evidence of invasion

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Pai RK, Beck AH, Norton JA, Longacre TA (2009)
Appendiceal mucinous neoplasms: clinicopathologic study of 116 cases with analysis of factors predicting recurrence.
Am J Surg Pathol 33: 1425-39



. Most are low-grade; high-grade cytology and architectural complexity are only compatible with a diagnosis of adenoma if the lesion resembles an adenoma of the colon and the muscularis mucosae is clearly intact. The designation of adenoma should imply that the lesion is curable by complete excision
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Carr NJ, Sobin LH (1996)
Unusual tumors of the appendix and pseudomyxoma peritonei.
Semin Diagn Pathol 13: 314-25




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Pai RK, Longacre TA (2005)
Appendiceal mucinous tumors and pseudomyxoma peritonei: histologic features, diagnostic problems, and proposed classification.
Adv Anat Pathol 12: 291-311



. An alternative diagnosis, such as low-grade appendiceal mucinous neoplasms(LAMN), is appropriate if there is any doubt. In particular, the presence of any mucin outside the appendix (even if the mucin is acellular) is incompatible with a diagnosis of adenoma
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Pai RK, Beck AH, Norton JA, Longacre TA (2009)
Appendiceal mucinous neoplasms: clinicopathologic study of 116 cases with analysis of factors predicting recurrence.
Am J Surg Pathol 33: 1425-39



. The classification of appendiceal adenomas is the same as that in the colon (tubular adenoma , tubulovillous adenoma and villous adenoma ). The commonest premalignant lesion of the appendix is the sessile serrated adenoma/polyp
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Pickhardt PJ, Levy AD, Rohrmann CA, Kende AI (2002)
Primary neoplasms of the appendix manifesting as acute appendicitis: CT findings with pathologic comparison.
Radiology 224: 775-81



, probably reported in the past as hyperplastic polyps or diffuse hyperplasia. In fact, although hyperplastic polyps of the appendix do occur, they are relatively unusual. A lesion that has villous structures, irregularly branched crypts or dilation at the base of the crypts is probably a sessile serrated adenoma/polyp, not a hyperplastic polyp. Traditional serrated adenomas and mixed hyperplastic adenomatous polyps form a significant proportion of lesions; the diagnostic criteria are the same as elsewhere in the large intestine
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Carr NJ, Mahajan H, Tan KL, Hawkins NJ, Ward RL (2009)
Serrated and non-serrated polyps of the colorectum: their prevalence in an unselected case series and correlation of BRAF mutation analysis with the diagnosis of sessile serrated adenoma.
J Clin Pathol 62: 516-8




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Yantiss RK, Panczykowski A, Misdraji J, Hahn HP, Odze RD, Rennert H, Chen YT (2007)
A comprehensive study of nondysplastic and dysplastic serrated polyps of the vermiform appendix.
Am J Surg Pathol 31: 1742-53



. We no longer recommend the use of “cystadenoma” as a diagnostic term at this site, since cystic change does not indicate a separate disease category
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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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By analogy with the rest of the large intestine, an adenoma–carcinoma sequence is assumed to occur in the appendix; the finding of a residual adenoma in some cases of adenocarcinoma supports this contention

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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



. A few adenocarcinomas appear to arise from goblet cell carcinoid tumours
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Burke AP, Sobin LH, Federspiel BH, Shekitka KM, Helwig EB (1990)
Goblet cell carcinoids and related tumors of the vermiform appendix.
Am J Clin Pathol 94: 27-35




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Carr NJ, Sobin LH (1995)
Epithelial noncarcinoid tumors and tumor-like lesions of the appendix.
Cancer 76: 2383-4



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