Types of Melanoma
There are four basic types of melanoma which differ in frequency and location in the body. At one time, the types were considered to carry different levels of risk. However, more current guides to risk indicate that one type of melanoma is not inherently more dangerous than another. They all pose the same level of risk, based on the following factors:
Superficial spreading melanoma is the most common type of melanoma, representing about 70% of all cases. As its name suggests, it spreads along the epidermis for a period of months to years before penetrating more deeply into the skin. The melanoma appears as a flat or barely raised lesion, often with irregular borders and variations in color. Lesions most commonly appear on the trunks of men, the legs of women, and the upper back of both sexes. The earliest sign of a new superficial spreading melanoma is darkening in one part of a pre-existing mole or the appearance of a new mole on unaffected normal skin.
Nodular melanoma represents 15 to 30% of all melanomas. It grows deeper more quickly than other types of melanoma, and is found most often on the trunk or head and neck. The melanoma usually appears as a blue-black, dome-shaped nodule, although 5% of lesions are pink or red. Nodular melanoma is more common in men than women.
Lentigo maligna melanoma arises from a pre-existing lentigo, rather than a mole, and accounts for approximately 5% of all melanoma cases. This type of melanoma typically takes many years to develop. It occurs most often in older adults, usually on the face and other chronically sun-exposed areas. These melanomas are generally large, flat, tan-colored lesions containing differing shades of brown, or as in other melanomas, black, blue, red, gray, or white.
Acral lentiginous melanoma accounts for less than 5% of all melanomas but is the most common melanoma in African Americans and Asians; although this may also occur in light-skinned (Caucasian) individuals. Acral comes from the Greek word akron, meaning extremity, and the disease typically appears on the palms, soles, or under the nails. Lesions are usually tan, brown, or black, with variations in color and irregular borders. Because of the misconceptions that melanomas only occur in sun-exposed areas, and that dark-skinned and Asian people are not at risk for melanoma, these melanomas are often discovered later than other forms of melanoma. A tendency to mistake the early signs of acral lentiginous melanoma for bruises or injuries to the palms, soles, or nailbeds may further delay diagnosis.