Anus & perianal area
Other tumors
Melanoma
Author: Nat Pernick, M.D.
Last author update: 1 April 2005
Last staff update: 20 September 2023 (update in progress)
Copyright:2002-2023, PathologyOutlines.com, Inc.
PubMed Search: Melanoma anal "loattrfree full text"[sb]
Table of Contents
Definition / general | Prognostic factors | Case reports | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Differential diagnosisCite this page: Pernick N. Melanoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/anusmelanoma.html. Accessed September 28th, 2023.
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
- Adenocarcinoma: with melanin containing tumor cells (rare)
- Lymphoma
- Squamous cell carcinoma, poorly differentiated
