Melanoma classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Classification of Melanoma

• Most common subtype
• Usually affects sun exposed sites among both men and women aged 50-70 years
• Characterized by presence of abundant junctional intraepidermal spread of malignant melanocytes

Subtype	Frequency	Clinical Features
Common Subtypes
Nodular melanoma	15-25%	Second most common subtype Usually affects sun exposed sites among both men and women aged 50-70 years Characterized by absence of junctional intraepidermal spread of malignant melanocytes
Acral lentiginous melanoma	5%	Not associated with chronic ultraviolet exposure Affects the extremities among inidividuals of all races Common among elderly Caucasian and non-Causasian individuals
Lentigo maligna melanoma	1-5%	Preceded by lentigo maligna Common among elderly Caucasian patients Usually appears as a flat, non-palpable lesion that affects sun exposed sites, especially the head and neck (extremities less common)
Non-cutaneous melanoma	5%	Melanoma that does not affect the skin Usually affects the eye (ocular melanoma) or the mucus membranes (mucosal melanoma)
Less Common Subtypes
Spindle cell melanoma	Rare	Lesion typically amelanotic Appears indolent but is highly infiltrative Characterized by local recurrence and perineurial spread Usually affects males aged 60-70 years in sun exposed sites May be de novo or associated with a pre-existing melanoma Has several subtypes: Pure: paucicellular Desmoplastic-neurotropic melanoma: characterized by neurotropism Pure neutrocropic: no desmoplasia with spindle cell melanoma of neurotropic phenotype Mixed/Combined: epithelial and spindle cells
Nevoid melanoma	Rare	Lesion has features of both melanoma and melanocytic nevus on histopathological analysis Clinical features resemble those of typical melanoma
Spitzoid melanocytic neoplasm	Rare	Lesion has features of both melanoma and Spitz tumor Typically affects sun exposed sites among children and young adults, but adults with Spitz tumors are more often diagnosed with Spitzoid melanoma Compared to benign Spitz tumors, Spitzoid melanomas are usually large (>5 mm)
Angiotropic melanoma	Rare	Lesion characterized by angiotropism, whereby melanoma grows in proximity (within 1-2 mm) to blood and/or lymphatic tissue but no tumor within the vascular lamina itself The tumor may originally be another subtype of melanoma Clinical features similar to typical melanoma
Blue nevus-like melanoma	Rare	Melanoma that develops from a pre-existing blue nevus One of the rarest forms of melanoma Appear as a blue nevus that has recently been rapidly expanding with irregular contours Typically affects middle-aged men
Composite melanoma	Rare	Melanoma that develops in proximity to other pre-existing epithelial malignancies (e.g. basal/squamous cell carcinoma) May be characterized by one of the following: Collision tumor: Collision of melanoma and another nearby malignant tumor Colonization: Colonization of melanocytes in a tumor Combined: Two distinct tumors appear to have mixed features of the melanoma and the other tumor Biphenotypic: One tumor that has features of melanoma and another epithelial malignancy