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Anus and perianal area

Carcinoma

Squamous cell carcinoma


Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 16 April 2013, last major update April 2005
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

General
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● Includes variants formerly called cloacogenic (obsolete term for basaloid features), basaloid, mucoepidermoid carcinoma
● Usually middle-aged patients, predominantly women (60-80%), present with rectal bleeding, pain or mass
● WHO recommends generic term “squamous cell carcinoma” be used for all squamous tumors, since no significant prognostic differences between subtypes, most tumors are mixtures of various subtypes, and reproducibility is low; however, additional comments on histologic features may be helpful
● Prominent basaloid features and small tumor cell size associated with high risk HPV
● Mucinous microcysts: poorer prognosis than standard squamous cell carcinoma; have well formed cystic spaces containing PAS+ or Alcian blue+ mucin

Gross description
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● Anal canal tumors are nodular, ulcerated, 3-4 cm or more, invade deeply into wall and spread proximally and distally into submucosa of distal rectum and proximal anus

Micro description
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● Variable features
● Resembles counterpart in skin or upper aerodigestive tract (keratinizing / well differentiated)
● May have glandular differentiation
● May be basaloid with plexiform pattern and palisading of small undifferentiated cells around the border and central necrosis of tumor nodules (also mitotic figures, invasion, desmoplastic stroma)
● May have massive eosinophilic infiltration, mucoepidermoid features, poorly differentiated morphology
● Often replaces crypts of adjacent rectal mucosa
● Often adjacent dysplastic changes

Differential diagnosis
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Basal cell carcinoma: fewer mitotic figures, smaller cells, less “flagrant” invasion

End of Anus and perianal area > Carcinoma > Squamous cell carcinoma


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