Melanoma

Four Major Types of Melanoma

Superficial spreading melanoma: The most common type; lesions are usually flat, irregular in shape, and contain varying shades of black and brown. It can occur at any age.
Lentigo maligna melanoma: Usually affects the elderly; involves large, flat, brownish lesions
Nodular melanoma: Can be dark blue, black, orreddish-blue, but may have no color at all. It usually starts as a raised patch.
Acral lentiginous melanoma: The least common type; typically affects the palms, soles of the feet, or under finger and toenails (AAD, 2010).

Melanoma

Less common than other types, melanoma is by far the most dangerous, causing about 75 percent of all skin cancer-related deaths (American Melanoma Foundation, 2009). It occurs in the skin cells that create pigment, and it creates moles or lesions that follow an ABCDE pattern in their irregularities:

asymmetrical shape
border irregularities
color
diameter
evolution of the lesion

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http://en.wikipedia.org/wiki/Melanoma