The American Cancer Society estimates that in 2008, nearly 62,500 people will be diagnosed with melanoma of the skin. While melanoma accounts for less than 5 percent of skin cancers, it is far more serious than other skin cancers if not detected and treated early.
Where Melanoma Begins
Melanoma is a type of cancer that arises in melanocytes, cells in the top layer of skin (called the epidermis) that produce the pigment melanin and cause skin to become tan when exposed to ultraviolet (UV) light from the sun. Melanocytes occasionally group together to form a normal mole (also called a nevus) or an irregular mole (a dysplastic nevus), which can become cancerous. Skin melanomas often look asymmetrical, have a ragged or blurred border, and are dark in color. Many are usually wider than a pencil eraser, but improved surveillance allows physicians to detect smaller melanomas. Rare melanomas contain no pigment, and can appear as pink nodules on the skin.
Melanoma also can begin in other pigmented tissues, such as the eye or the membranes lining the sinuses, anus, and vagina.
Types of Skin Melanoma
There are two main classifications of primary melanoma. In situ melanoma is limited to the skin and does not metastasize to other parts of the body. Melanoma can penetrate the lower layer of the skin, which is called the dermis. Invasive, or metastatic, melanoma is more likely to spread to the lymph nodes and beyond, particularly if it is over one millimeter thick. The deeper the melanoma penetrates the skin, the more likely it is to spread to other parts of the body, including regional and distant lymph nodes, the lungs, liver, brain, bones, and gastrointestinal tract.
Although melanoma usually shows up on parts of the body exposed to the sun, such as on the trunk and the arms and legs, it can develop on any part of the body.
