Primary Mucosal Melanoma: Uncommonly Described Entity

Malignant melanoma arises by malignant transformation of the normal melanocytes. Distribution of malignant melanoma includes cutaneous (91.2%), ocular (5.3%), mucosal (1.3%), and unknown primary site (2.2%). Because of rarity and clinical challenges arising from different anatomic location, our understanding for the optimal management of mucosal melanoma remains limited. Malignant melanoma can arise from the mucosal epithelium of respiratory, alimentary, and genitourinary tracts, all of which contain melanocytes. The most common sites for primary mucosal melanoma include head and neck followed by anorectal, and vulvovaginal regions (55, 24, and 18%, respectively). Rarer sites are urinary tract, gallbladder, and small intestine.

Although melanocytes share same embryologic origin, mucosal melanomas behave more aggressively and have many different characteristics compared to cutaneous melanomas. Mucosal melanomas are multifocal in 20% cases, while cutaneous melanomas are multifocal in 5%. 40% of mucosal melanomas are amelanotic, while <10% of cutaneous melanomas. In the following section we described this uncommonly presented entity. 5 year survival for mucosal melanoma is 25%, while that for cutaneous melanoma it is 80.8%.

Etiopathogenesis

Mucosal melanoma arises in non-sun exposed parts of the body and risk factors are not properly defined. Incidence increases with age and > 65% of patients are older than 60 years . The difference between white and black population is less pronounced compared to cutaneous melanoma and mucosal melanomas are approximately twice higher among whites compared to blacks. The higher incidence in females compared to males is because of the predominance of genital tract melanomas in females, which account for 56.5% of mucosal melanomas among them . There is no difference in rates between genders for extragenital mucosal melanomas.