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Anus and perianal area

Other malignancies

Melanoma


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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● Relatively rare; 10% as common as squamous cell carcinoma
● Often mistaken for hemorrhoids, causing late diagnosis
● 5 year survival 15%
● Must have high index of suspicion to diagnose

Prognostic factors
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● Prognosis related to tumor size and depth of invasion (2 mm or less have excellent prognosis)

Case reports
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● 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
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● Single or multiple, large polypoid mass, 80% pigmented, grows near dentate line

Micro description
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● 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)

Micro images
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Melanoma at anorectal junction


68 year old with lesion resembling a hemorrhoid, contributed by Dr. Marino E. Leon, Moffitt Cancer Center, Tampa, Florida (USA)

Positive stains
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● HMB45, S100, MelanA / Mart1

Negative stains
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● Keratin

Differential diagnosis
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Adenocarcinoma: with melanin containing tumor cells (rare)
Lymphoma
Squamous cell carcinoma, poorly differentiated

End of Anus and perianal area > Other malignancies > Melanoma


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