Anus & perianal area


Squamous cell carcinoma

Last author update: 31 March 2021
Last staff update: 13 March 2023 (update in progress)

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

Raul S. Gonzalez, M.D.
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Cite this page: Gonzalez RS. Squamous cell carcinoma. website. Accessed March 22nd, 2023.
Definition / general
  • Primary squamous cell carcinomas of anus
Essential features
  • 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

Contributed by Raul S. Gonzalez, M.D.

Squamous cell carcinoma

Sample pathology report
  • Anus, mass, biopsy:
    • Focal invasive squamous cell carcinoma, arising in a background of high grade squamous intraepithelial lesion (AIN 3)
  • Anus, resection:
    • Squamous cell carcinoma, moderately differentiated (see synoptic report)
Differential diagnosis
Board review style question #1

    Which of the following is true about anal squamous cell carcinoma?

  1. Cases above the dentate line are more common in men
  2. Cases below the dentate line are more common in elderly patients
  3. Patients with HIV have a worse prognosis
  4. Vast majority are purely basaloid
Board review style answer #1
C. Patients with HIV have a worse prognosis

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Reference: Squamous cell carcinoma
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