Anus & perianal area

Other tumors

Melanoma



Topic Completed: 1 April 2005

Minor changes: 15 October 2021

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PubMed Search: Melanoma anal "loattrfree full text"[sb]

Nat Pernick, M.D.
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Cite this page: Pernick N. Melanoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/anusmelanoma.html. Accessed January 21st, 2022.
Definition / general
  • Relatively rare; 10% as common as squamous cell carcinoma
  • Often mistaken for hemorrhoids, causing late diagnosis
  • Five year survival 15%
  • Must have high index of suspicion to diagnose
Prognostic factors
  • Prognosis related to tumor size and depth of invasion (2 mm or less has excellent prognosis)
Case reports
  • 59 year old man with rectal bleeding and an 11 year old history of a malignant fibrous histiocytoma in the deep soft tissue of calf (Arch Pathol Lab Med 1995;119:285)
Gross description
  • Single or multiple, large polypoid mass, 80% pigmented, grows near dentate line
Microscopic (histologic) description
  • Resembles mucosal melanoma
  • Pigmented epithelioid or spindle cells in nesting pattern, usually with junctional component with lentiginous appearance (may be absent in ulcerated tumors)
  • Invades crypts in pattern similar to lymphoma
  • Rarely desmoplastic (Hum Pathol 1985;16:1277)
Microscopic (histologic) images

Contributed by Marino E. Leon, M.D.

68 year old with lesion resembling a hemorrhoid

Positive stains
Negative stains
Differential diagnosis
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