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Important risk factors for cutaneous melanoma include light skin, hair, and eyes; a history
of sun sensitivity; high exposure to intermittent intense sunlight, especially during
childhood; impaired DNA repair of UV injury, as in xeroderma pigmentosum; and

The interaction between melanoma and vitiligo remains to be clarified. Some authors
postulate that patients with vitiligo have a lower incidence of melanoma,35 whereas others
report that vitiligo is more common in patients with melanoma than in age-matched control
malanoma or melenoma.

Melanomas commonly arise from preexisting nevi but may arise de novo from epidermal
melanocytes. Common sites are the head, the neck, and the trunk in males and the extremities,
especially the legs.

Melanoma may also arise in congenital melanocytic nevi [see Subsection XI], especially
those greater than 20 cm in diameter (often termed giant congenital nevi when involving a
large surface area of the body). The estimated occurrence is five to 20 percent during a
lifetime, but such malignant transformation usually occurs by 10 years of age.37 Characteristic histologic
features of giant congenital nevi include deep dermal extension of melanocytes
with adnexal involvement and neural differentiation. The potential risk of melanoma in smaller
congenital pigmented nevi, which may lack these histologic features.

Several clinical types of melanoma have been recognized. Lentigo maligna melanoma and
superficial spreading melanoma are characterized by an early horizontal growth phase in the
epidermis, which is followed after a variable period by dermal invasion that results in a
nodular lesion. Acral lentiginous melanoma occurs on palmar, plantar, and mucosal surfaces.

Superficial spreading melanoma, the most common type of melanoma, begins as a small,
irregular, brown-pigmented lesion with various shades of red, white, and blue.
There is diffuse intraepidermal distribution of relatively monomorphous, large malignant
melanocytes in noninvasive areas. After a variable period of superficial growth, usually
ranging from one to five years, papules or nodules signifying vertical growth appear.

Acral lentiginous melanoma, the most common form of melanoma in blacks, occurs on the
non–hair-bearing sites, such as the soles, the palms, the digits, subungual and periungual
areas, and mucosal surfaces. Lesions are more common in patients older than 60 years.

In 34 of 35 cases of nonmucosal acral lentiginous melanoma reviewed in one study, the
lesions were located on the soles. Twenty-five percent of the patients.

Nodular melanoma first appears as a rapidly growing papule or nodule with a smooth, scaly,
eroded.

Desmoplastic melanoma, a rare but distinct type of melanoma that may be mistaken for
invasive fibromatosis or fibrosarcoma, consists of a deeply infiltrating nodule.