Mucosal melanoma

Mucosal melanomas are non-cutaneous malignant melanomas arising from mucosal epithelium.

This article is an overview; for specific locations in the body, see their respective articles: sinonasal mucosal melanoma.

Epidemiology

Mucosal melanomas are rare, comprising about 1% of all melanomas . The median age of diagnosis is 70 years, higher than that of cutaneous melanomas . There are no known environmental risk factors.

Pathology

Etiology

The histogenesis of melanomas, including mucosal melanomas, is from melanocytes.

Location

Mucosal melanoma can arise from any mucosal epithelium in the body. The most common locations are the following :

head and neck (55%), most commonly sinonasal, followed by oral cavity
anorectum (24%)
female genital tract (18%)
urinary tract (3%)

Macroscopic appearance

Up to 40% of mucosal melanomas are amelanotic, meaning the tumors are at least partially devoid of the melanin pigment .

Staging

Staging system differs depending on the primary site of disease . Head and neck tumors are staged by the American Joint Committee on Cancer TNM system. Melanomas of the external lip and vulva are staged as cutaneous melanomas. Anorectal and vaginal tumors do not have a specifically designed staging system but can be categorized by the following system originally introduced by Ballantyne for the head and neck :

stage I: clinically localized disease
stage II: regional lymph node involvement
stage III: distant metastases

Radiographic features

MRI

T1 hyperintensity is characteristic, reflecting melanin, but not universal, likely due to amelanosis .

Treatment and prognosis

Treatment typically consists of surgical excision and radiation therapy. Decisions for systemic chemotherapy are based on limited evidence, often extrapolated from cutaneous melanoma. The prognosis is poor, with a five-year overall survival of 25% .