Melanomas fall into four basic categories. Three of them begin in situ — meaning they occupy only the top layers of the skin — and sometimes become invasive; the fourth is invasive from the start. Invasive melanomas are more serious, as they have penetrated deeper into the skin and may have spread to other areas of the body.
Superficial spreading melanoma is by far the most common type, accounting for about 70 percent of all cases. This is the one most often seen in young people. As the name suggests, this melanoma grows along the top layer of the skin for a fairly long time before penetrating more deeply.
The first sign is the appearance of a flat or slightly raised discolored patch that has irregular borders and is somewhat asymmetrical in form. The color varies, and you may see areas of tan, brown, black, red, blue or white. This type of melanoma can occur in a previously benign mole. The melanoma can be found almost anywhere on the body, but is most likely to occur on the trunk in men, the legs in women, and the upper back in both.
Lentigo maligna is similar to the superficial spreading type, as it also remains close to the skin surface for quite a while, and usually appears as a flat or mildly elevated mottled tan, brown or dark brown discoloration. This type of in situ melanoma is found most often in the elderly, arising on chronically sun-exposed, damaged skin on the face, ears, arms and upper trunk. Lentigo maligna is the most common form of melanoma in Hawaii. When this cancer becomes invasive, it is referred to as lentigo maligna melanoma.
Acral lentiginous melanoma also spreads superficially before penetrating more deeply. It is quite different from the others, though, as it usually appears as a black or brown discoloration under the nails or on the soles of the feet or palms of the hands. This type of melanoma is sometimes found on dark-skinned people, and tends to advance more often than superficial spreading melanoma and lentigo maligna because it is detected later. It is the most common melanoma in African-Americans and Asians, and the least common among Caucasians.
Nodular melanoma is usually invasive at the time it is first diagnosed. The malignancy is recognized when it becomes a bump. It is usually black, but occasionally is blue, gray, white, brown, tan, red or skin tone.
The most frequent locations are the trunk, legs, and arms, mainly of elderly people, as well as the scalp in men. This is the most aggressive of the melanomas, and is found in 10 to 15 percent of cases.