744 Clinicopathologic and Immunohistochemical Features of Anorectal Melanoma: A Retrospective Study

Document Type

Conference Proceeding

Publication Date

3-23-2026

Publication Title

Lab Invest

Keywords

melan A, adult, aged, anorectal cancer, anorectal melanoma, clinical article, conference abstract, delayed diagnosis, diagnosis, epithelioid histiocyte, female, follow up, hemorrhoid, histology, human, immunofluorescence, immunohistochemistry, immunophenotyping, male, middle aged, retrospective study, treatment outcome, tumor volume

Abstract

Disclosures: Zoonish Ashfaq: None; Alka Rani: None; Pierre Tran: None; Antonio Lira Diaz: None; Nasir Ud Din: None; Beena Ahsan: None Background: Anorectal melanoma is a rare and aggressive malignant neoplasm that accounts for less than 1% of all anorectal malignancies. Because of its nonspecific clinical presentation and morphologic heterogeneity, diagnosis is often delayed and prognosis remains poor. A detailed understanding of its clinicopathologic and immunohistochemical features is essential for accurate diagnosis and prognostication. This study aims to describe the clinicopathologic characteristics and immunoprofile of anorectal melanoma in a single-institution cohort. Design: We conducted a retrospective clinicopathologic review of anorectal melanoma cases diagnosed at a single institution between 2019 and 2024. Clinical data, including age, sex, and presenting symptoms were collected from medical records. Histologic features such as macroscopic appearance and tumor size were recorded from pathology reports. Morphologic characteristics, presence of necrosis or ulceration, and immunohistochemical staining results for HMB45, Melan-A, SOX10, and S100 were reviewed. Follow-up information was obtained to assess patient outcomes (alive versus deceased at last follow-up). Descriptive statistics were used to summarize clinicopathologic parameters. Results: A total of 76 cases of anorectal melanoma were identified. Patients ranged in age from 28 to 84 years (mean, 57 years) with a male-to-female ratio of 1.8:1. The most common presenting symptom was a mass-like feeling (71%), followed by anal bleeding and pain. Grossly, 71% of tumors appeared polypoid/hemorrhoid-like, followed by large anal masses or pigmented lesions. Microscopically, tumors were composed of nests of spindle to epithelioid cells, and 60% showed surface ulceration. Immunohistochemical staining was positive for HMB45 in 91%, Melan-A in 96%, SOX10 in 100%, and S100 in 100% of cases. Follow-up data were available for 30 patients; of these, 4 (13%) were alive, 1 (3%) was alive with disease, and 25 (83%) had died at last follow-up. The mean follow-up duration was 15 months. Conclusions: Anorectal melanoma predominantly affects middle-aged adults, with a slight male predominance, and typically presents with nonspecific symptoms such as an anal mass, often resulting in delayed diagnosis. Despite variable morphologic features, recognition of its characteristic immunophenotype is critical for accurate diagnosis. The overall prognosis remains poor, highlighting the need for early recognition and multidisciplinary management.

Volume

106

Issue

3

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