In situ melanoma is confined to the epidermis or upper layer of the skin. It will not spread once the lesion (raised portion of the skin) has been removed.
Invasive melanoma has advanced into the deeper layers of the skin called the dermis and the subcutis. It may also spread to the lymph nodes as well as to the lungs, liver, brain, bones, and digestive tract. As a rule, if a melanoma is thicker than one millimeter, it is more likely to invade other parts of the body.
There are four different types of melanoma.
Superficial spreading melanoma may move to other cells but stays on the surface layer of the skin. This is the most common type of melanoma (70 percent of all cases) and usually affects younger people. It appears as a flat or slightly raised discolored patch of skin with irregular borders and a varied coloration, with areas of tan, brown, black, red, blue or white. Superficial spreading melanoma is usually found on the trunk, legs, or upper back.
Lentigo maligna also remains close to the surface of the skin and is a flat or mildly elevated growth ranging from in color from tan to dark brown. It usually affects elderly people who have sun damaged skin on their face, ears, arms and upper torso. This type of cancer can become invasive. When it does, it is referred to as lentigo maligna melanoma.
Acral lentiginous melanoma 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 can spread fairly quickly.
Nodular melanoma is an invasive melanoma that shows up as a black bump on the skin but occasionally appears blue, gray, white, brown, tan, or red. It can even be the same color as the surrounding flesh. This form of melanoma is frequently found in elderly patients on the trunk, legs, and arms, and on the scalp in men.