Types of Melanoma
The appearance and growth of melanoma will differ depending on the morphologic type:
Superficial spreading melanoma
Superficial spreading melanoma is the most common type of melanoma, representing approximately 70% of all melanomas. This melanoma goes through a prolonged (years) horizontal growth pattern on the skin before becoming invasive. Superficial spreading melanomas are flat or slightly elevated brown lesions with black, blue or pink discoloration which are typically greater than 6 mm in diameter and have irregular asymmetric borders. These melanomas may be found on any body surface, especially the head, neck, and trunk of males and the lower extremities of females.
Nodular melanoma represents about 15% of all melanomas and becomes invasive soon after first appearing. A nodular melanoma typically looks similar to a blood vessel growth, presenting as a dark brown-to-black papule or dome-shaped nodule; however, 5% of nodular melanomas are amelanotic (see below). These melanomas are commonly found on all body surfaces, especially the trunk of males.
Acral-lentiginous melanoma represents approximately 8% of all melanomas and is the most common melanoma in dark-skinned people. Acral-lentiginous melanomas represent up to 70% of melanomas in blacks and up to 46% in Asians. This type can occur on the palms, soles and nail beds (subungual). Like nodular melanoma, acral-lentiginous melanoma is extremely aggressive, with rapid progression from the horizontal to vertical growth phase.
Lentigo maligna melanoma
Lentigo maligna melanoma accounts for approximately 5% of melanomas. Lentigo maligna melanomas are typically found on sun-exposed areas of the skin in adults and are clearly linked to exposure to the sun. Often many years pass between the first appearance of this melanoma and when it becomes invasive. The precursor lesion is typically greater than 3 cm in diameter, and, upon becoming invasive, develops a dark brown-to-black color or raised blue-black nodule.
Amelanotic melanoma is rare and challenging to diagnose because there is an absence of pigmentation (color). However, hallmark traits of melanoma, such as changes in size, borders, and symmetry, are present in this melanoma.
Desmoplastic melanoma is rare, representing approximately 1.7% of all melanomas. This type of melanoma is locally aggressive and difficult to diagnose both clinically and microscopically. The majority of these tumors occur on the head and neck of elderly patients and one half are amelanotic.