Anus & perianal area

Carcinoma

Adenocarcinoma


Editorial Board Member: Xiaoyan Liao, M.D., Ph.D.
Deputy Editor-in-Chief: Aaron R. Huber, D.O.
Raul S. Gonzalez, M.D.

Last author update: 23 May 2023
Last staff update: 23 May 2023

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PubMed Search: Adenocarcinoma anus

Raul S. Gonzalez, M.D.
Page views in 2023: 6,631
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Cite this page: Gonzalez RS. Adenocarcinoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/anusadenocarcinoma.html. Accessed May 19th, 2024.
Definition / general
  • Rare adenocarcinoma that primarily involves the anal canal (not rectal adenocarcinomas with downward spread)
Essential features
  • Rare, primary gland forming malignancy of the anus
  • May arise from anal glands, from congenital anorectal duplications or along a fistula tract
  • Must be distinguished from adenocarcinoma secondarily involving anus (e.g., rectal carcinoma)
Terminology
  • Also known as perianal adenocarcinoma or perianal gland adenocarcinoma
  • The term anal duct adenocarcinoma is not recommended
ICD coding
  • ICD-10: C21.0 - malignant neoplasm of anus, unspecified
Epidemiology
Sites
  • Anus (by definition)
Pathophysiology
Etiology
Diagrams / tables

Images hosted on other servers:
Classification of anal adenocarcinoma

Classification
of anal
adenocarcinoma

Clinical features
  • May present in fistula tract or as a vaginal cyst
  • Often a long history of perianal fistulas, abscesses, surgery
  • Indolent course with gradual progression
Diagnosis
  • Gross examination and tissue sampling
Prognostic factors
Case reports
Treatment
Clinical images

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Irregular mucosa and angioectasia

Irregular mucosa and angioectasia

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
Gross images

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Anal canal cancer

Anal canal cancer

Microscopic (histologic) description
  • Adenocarcinomas with an intestinal type appearance involving the anus are likely of rectal origin and should be regarded as such
  • True anal gland adenocarcinomas form haphazardly dispersed small glands with scant mucin production that invade the wall of the anorectal area without an intraluminal component (Cancer 2001;92:2045)
  • Fistula associated adenocarcinomas are often mucinous (> 50% of tumor volume consists of mucin); granulomatous reaction to mucin may be present
  • May contain melanin pigment, perhaps due to tumor cell phagocytosis of melanin from melanocytes (Am J Surg Pathol 1981;5:711)
  • Single neoplastic cells may colonize the overlying and adjacent squamous mucosa (Paget disease)
  • HPV related cases show papillary or villiform structures lined by columnar cells that often contain abundant mucin (Mod Pathol 2020;33:944)
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.
Anal adenocarcinoma

Infiltrating, gland forming

Infiltrating glands

Infiltrating glands

Mucinous and signet ring

Mucinous and signet ring

Fistula tract associated

Fistula tract associated

Negative stains
Molecular / cytogenetics description
Sample pathology report
  • Anus, resection:
    • Anal adenocarcinoma, moderately differentiated (see synoptic report)
Differential diagnosis
  • Anal mucoepidermoid carcinoma:
  • Secondary involvement by rectal adenocarcinoma:
    • More common than primary anal adenocarcinoma
    • Usually CK20+
    • May require clinical correlation
  • Squamous cell carcinoma:
    • Far more common at this location
    • Distinguishable microscopically
  • Secondary involvement by gynecologic tract adenocarcinoma:
    • In women, vaginal or vulvar adenocarcinomas may directly extend into anus
    • Positivity for ER or PR may support this interpretation
Board review style question #1

Which of the following is true about primary anal adenocarcinoma?

  1. Advanced stage cases paradoxically have a better prognosis
  2. It can arise in a fistula tract
  3. It is more common in women
  4. It is more common than secondary involvement by rectal carcinoma
Board review style answer #1
B. It can arise in a fistula tract. This may occur in patients with Crohn's disease. Overall, anal adenocarcinoma is more common in men and advanced stage indicates poor prognosis. It is rare and secondary anal involvement by rectal carcinoma is more common.

Comment Here

Reference: Anal adenocarcinoma
Board review style question #2
Primary anal adenocarcinoma is usually positive for which of the following immunohistochemical stains?

  1. CDX2
  2. CK7
  3. CK20
  4. p16
Board review style answer #2
B. CK7. Only rare cases of anal adenocarcinoma are positive for p16. Rectal carcinoma involving the anus is positive for CDX2 and CK20.

Comment Here

Reference: Anal adenocarcinoma
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