Types of Melanoma
There are four types of melanoma. Three types begin as tumors confined within a site (in-situ), usually within the upper portion of the epidermis. The fourth type is very invasive and quickly penetrates into the lower skin layers and spreads to other areas within the body.
Superficial spreading melanoma (SSM) accounts for more than two-thirds of all melanoma cases. SSM changes slowly, usually over a period of one or more years. It often appears as a dark, flat, or slightly raised mark on the skin with variegated colors. Its borders are irregular, with indentations or notches. In women, SSM often occurs on sun-exposed surfaces of the skin over the shin. In men, it occurs most often on the back of the torso and along the front of the legs. SSM can also occur on the soles of the feet. Superficial spreading melanoma mostly appears after puberty. In young people, this is the most common type of melanoma.
Superficial spreading melanoma has two growth phases. The radial phase involves expansion of the lesion through the epidermis (upper skin layer). In the early radial phase, the lesion is thin, and it can remain in this phase for months or years. This is the less threatening of the two phases, because once the melanoma enters into the vertical growth stage, the prognosis worsens. In the vertical growth phase, the melanoma grows into the dermis (deep skin layer) and underlying structures. At this point, the cancer is a dangerous malignancy and has the ability to invade other tissues and metastasize.
Nodular melanoma (NM) represents 15 to 20 percent of cases. It arises very rapidly, is the most aggressive type of melanoma, and is the second most common type. Unlike superficial spreading melanoma, which tends to spread outward, nodular melanoma grows rapidly upward and inward. NM usually develops in unblemished skin rather than in a nevus. It is often in a fully invasive stage of growth when it is diagnosed.
NM has a typical skin cancer pattern. It is most common in light-skinned people and usually affects areas of skin that are frequently exposed to the sun (e.g., arms, legs, head, neck, and scalp). NM usually develops in middle-age.
NM characteristically appears as a uniformly black-colored nodule (small, knot-like bump), although the nodule also may be brown, blue, gray, tan, or even red. It feels very round, and the borders are smooth and regular. These lesions often are mistaken for blood vessel abnormalities because of their berry color and texture.
Acral lentigous melanoma (ALM) is the most common variant of skin cancer seen in dark-skinned people. This form of melanoma appears on the palms of the hands, the soles of the feet, or on nails. Lesions are usually brown, black, or multicolored with irregular borders, and flat or nodular.
When it develops on the nail, it usually involves the thumb or big toe and may be seen as a black linear band, often with a discolored surrounding cuticle. ALM may look like a bruise, blood blister, or brownish-black blotch on the toe or finger. Fortunately, ALM grows rather slowly spreads along the surface before penetrating the skin's deeper layers. ALM may involve only a part of the nail, or it may affect the entire nail and surrounding tissue. Lesions may have a streaked appearance with some parts having well-defined, highly irregular borders, and others having a blurred appearance.
Lentigo maligna melanoma (LMM) is the least common variant of melanoma. This type occurs most often on the nose and cheeks and it is more common in older patients, typically in people in their 70s. The lesions are flat and tan, brown, black, or other colors. The borders can be scalloped and convoluted, and they commonly grow to fairly large sizes (3 cm6 cm or larger). Like superficial spreading melanoma, lentigo maligna tends to spread slowly along the surface layers of the skin. Lentigo maligna does not tend to metastasize as some other melanomas do.