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WHO Classification of Tumours
Adenosquamous carcinoma
Region of the ampulla of Vater


A carcinoma composed of malignant glandular cells and malignant squamous cells.

Adenosquamous carcinoma of the ampulla of Vater
This unusual neoplasm represents 1% of all ampullary carcinomas and is characterized by a variable combination of two malignant components, one glandular and the other squamous, like adenosquamous carcinomas seen in other anatomic sites

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Song DE, Park JK, Hur B, Ro JY (2004)
Carcinoid tumor arising in a tailgut cyst of the anorectal junction with distant metastasis: a case report and review of the literature.
Arch Pathol Lab Med 128: 578-80

. Although the proportion of each component varies, the adenocarcinoma usually predominates, is well- to moderately differentiated, and of pancreatobiliary phenotype. The squamous carcinoma component is focally keratinizing and by convention should represent at least 25% of the tumour. In contrast, any amount of glandular differentiation suffices to designate a predominantly squamous neoplasm as adenosquamous carcinoma. In some cases, clear cells line the glands and are mixed with the squamous elements. A micropapillary pattern can be seen rarely
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Khayyata S, Basturk O, Adsay NV (2005)
Invasive micropapillary carcinomas of the ampullo-pancreatobiliary region and their association with tumor-infiltrating neutrophils.
Mod Pathol 18: 1504-11

. Some adenosquamous carcinomas arise from preexisting adenomas
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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