Melanoma may be classified into either cutaneous or non-cutaneous melanomas. The most common 4 subtypes of cutaneous melanoma include superficial spreading melanoma, nodular melanoma, acral lentiginous melanoma, and lentigo maligna melanoma. Less common subtypes of melanoma include desmoplastic/spindle cell melanoma, nevoid melanoma, spitzoid melanocytic melanoma, angiotropic melanoma, blue nevus-like melanoma, and composite melanoma.
Classification of Melanoma
Shown below is a table that demonstrates that various subclasses of melanoma:[1][2]
Subtype
Frequency
Clinical Features
Common Subtypes
Superficial spreading melanoma
70%
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
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 are 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
Desmoplastic/Spindle cell melanoma
Rare
Lesion typically amelanotic and has a morphology similar to a scar tissue
Appears indolent but is highly infiltrative
Characterized by local recurrence and perineural 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 neurotropic melanoma: 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 (epithelioid) 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
Appears 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
References
↑Schanderdorf D, Kochs C, Livingstone E (2013). Handbook of Cutaneous Melanoma: A Guide to Diagnosis and Treatment. Springer.CS1 maint: Multiple names: authors list (link)
↑Mooi W, Krausz T (2007). Pathology of Melanocytic Disorders 2nd Ed. CRC Press.