Mucosal melanoma: Review from a pathologist point of view

Mucosal melanomas (MuM) are rare malignant tumors arising from the epithelia lining the inner mucosal surfaces of the body. Unlike cutaneous melanoma, understanding of MuM is limited among pathologists and clinicians alike, primarily due to rarity of these tumors. MuM are characterized by genetic alterations quite distinct from cutaneous melanomas; however, their causative and promoting factors are unknown. These melanomas are characteristically diagnosed at a later stage due to their occult locations, leading to a worse prognosis. Dedicated staging systems for MuM exist only for sinonasal and conjunctival melanomas. Risk stratification of patients with MuM, particularly those arising from the anogenital area, is challenging. Recent studies have shown that minor modifications of the American Joint Committee on Cancer eighth edition cutaneous melanoma staging system can group patients fairly robustly; however, the proposed T-categorization systems have yet to be validated in larger cohorts. We summarize the demographic, clinical, histopathologic, and molecular features of common subtypes of MuM and highlight the outstanding needs in this field.