Four major clinicopathologic subtypes of primary cutaneous melanoma have been identified, although newer classifications of melanoma include location on chronically sun-exposed vs intermittently or non–sun-exposed skin and incorporate the presence of driver mutations in BRAF, NRAS, NF-1, and other oncogenes. Classic histopathologic melanoma subtypes include superficial spreading, nodular, lentigo maligna, and acral lentiginous.
Distinction among these subtypes is based on histologic growth pattern (predominantly junctional in lentiginous types, pagetoid in the superficial spreading subtype, and predominantly dermal in the nodular subtype), anatomic site, and degree of sun damage. The pattern of sun exposure varies between the types (chronic in the lentigo maligna subtype, intermittent in superficial spreading and nodular subtypes, and noncontributory in acral lentiginous and mucosal subtypes).
Superficial spreading melanoma accounts for most cutaneous melanomas and is the most common subtype in individuals aged 30-50 years, as well as in those with clinical atypical/dysplastic nevi. Nodular melanoma occurs in at least 10%-15% of cases. It is seen most commonly on the legs and trunk in men and women. Rapid growth occurs over weeks to months; this subtype is responsible for most thick melanomas. Lentigo maligna is the third most common subtype and is typically located on the head, neck, and arms (chronically sun-damaged skin) of fair-skinned older individuals (average age, 65 years).
Acral lentiginous melanoma is the least common subtype of melanoma in White persons and the most common subtype of melanoma in dark-skinned individuals. Due to delays in diagnosis, it is often associated with a worse prognosis.
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Cite this: William James. Fast Five Quiz: Malignant Melanoma - Medscape - Aug 21, 2020.