Anus & perianal area
Squamous cell carcinoma

Topic Completed: 1 December 2014

Minor changes: 16 November 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Squamous cell carcinoma [title] anus "loattrfree full text"[sb]

Raul S. Gonzalez, M.D.
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Cite this page: Gonzalez RS. Squamous cell carcinoma. website. Accessed January 22nd, 2021.
Definition / general
  • Most common carcinoma of anal tract
  • Increasing in incidence, although still relatively rare (incidence of < 1 per 100,000)
  • Can arise either above or below dentate line
  • WHO officially only recognizes "squamous cell carcinoma"
  • Basaloid variant has also been termed "cloacogenic" or "transitional"
  • "Mucoepidermoid carcinoma" may be used for tumors with prominent mucinous features, although the biology may be different (J Gastroenterol 2001;36:508)
  • Tumors above dentate line: more common in women, usually diagnosed in sixth decade
  • Tumors below dentate line: more common in men, usually diagnosed in third decade
Clinical features
  • Presenting symptoms include rectal bleeding, pain, mass
Prognostic factors
  • Surgery with chemoradiation
Gross description
  • 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
Microscopic (histologic) description
  • Resembles squamous cell carcinoma as seen elsewhere in body
  • Tumors often display multiple morphologic patterns, calling into question the utility of subdividing the entity
  • May be keratinizing (usually below the dentate line) or nonkeratinizing (anywhere, although tumors above dentate line are usually nonkeratinizing)
  • Basaloid subtype shows plexiform pattern and palisading of small undifferentiated cells around the border, with central necrosis of tumor nodules (also mitotic figures, invasion, desmoplastic stroma)
  • May have massive eosinophilic infiltration, mucoepidermoid features (with "mucinous microcysts") or poorly differentiated morphology
  • Can show "small cell" anaplastic features (but without evidence of neuroendocrine differentiation)
  • Often replaces crypts of adjacent rectal mucosa
  • May show overlying / adjacent dysplastic changes (anal intraepithelial neoplasia)
Microscopic (histologic) images

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Anal squamous cell carcinoma

Differential diagnosis
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