Morphologic and Immunohistochemical Characteristics of Anorectal Melanoma

Abstract

Anorectal melanoma is a rare aggressive disease. Due to its rarity and considerable histologic and immunohistochemical variabilities, misdiagnosis as lymphoma, carcinoma, sarcoma, and/or gastrointestinal stromal tumor is not uncommon, particularly in amelanotic cases. We reviewed histologic features and immunohistochemical stains of 19 anorectal melanoma cases. Histopathologic features were evaluated including junctional activity, melanin pigment, and morphologic features. Immunohistochemical stains were performed using Sox10, S100 protein, HMB-45, melan-A, CD56, and cytokeratins. Epithelioid histopathologic morphology was observed in 63.2% of the cases followed by 47.4% of the cases with spindle-cell, 26.3% with lymphoma-like, and 26.3% with pleomorphic morphologies. Junctional melanocytic activity was seen in almost half of the cases. Melanin pigment was absent (amelanotic) in nearly 40% of the cases. Immunohistochemically, diffuse positive expression of Sox10, S100 protein, melan-A, and HMB-45 was seen in 100%, 40%, 53.3%, and 38.5% of the cases, respectively. Cytokeratins were negative and CD56 was positive in 2 cases. These findings indicate that anorectal melanomas often show one or combined histolopathologic features without presence of melanin pigment and absence of junctional melanocytic activity. Anorectal melanoma should be kept in mind in the differential diagnosis of malignant neoplasms of anorectal region with epithelioid, spindle-cell, lymphoma-like, and pleomorphic morphologies. Sox10 immunohistochemistry stain can be used as a first-line screening tool to avoid extensive or unnecessary workups and/or potential misdiagnosis.

Gardner Syndrome imaging features in plain radiographs and computed tomography: a case report

“…For colorectal polyps, the treatment includes healthy diet, the use of nonsteroid ant inflammatory such as slindac or a Cox2 inhibitors like celecoxib, which can slow the growth of the polyps in the colon, and also surveillance by endoscopies and colonoscopies. If more than 20 polyps are observed, colon removal is recommended in order to reduce the risk of development of colon cancer [10].…”

Primary Dedifferentiated Amelanotic Anorectal Melanoma: Report of a Rare Case

“…It is presumed to arise from melanocytes in the basal layer of the stratified squamous epithelium. 23 Patients usually present with advanced disease in their sixth decade, which manifests as rectal bleeding or pain, a rectal mass, or anal pruritus, leading to the clinical impression of hemorrhoids. 3,27 Diagnosis relies on histomorphology and ancillary studies including immunohistochemistry and molecular analysis as stated above.…”

“…14,15,17 Yet, BRAF mutation occurs much less frequently in ARMs. 3,23 Instead, approximately 30% of ARM have confirmed KIT mutations 24,25 and a subset of tumors has been shown to harbor recurrent mutations in NF1 (20%), SF3B1 (20%), TP53 (20%), RAS (11%), and BRAF (<7%). 24 ARM with activating KIT mutations may respond to c-Kit inhibitor–based therapy, with improved patient survival at advanced tumor stages.…”

Clinical evidence, diagnostic approach and challenging therapeutic modalities for malignant melanoma of the anorectum

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