Melanoma is a serious form of skin cancer that starts in the pigment-producing skin cells called melanocytes. These cells become abnormal, grow uncontrollably, and aggressively invade surrounding tissues.

Melanoma can develop in an existing mole or other mark on the skin, but it often develops in unmarked skin. Early signs of melanoma are a change in a mole or other skin growth (such as a birthmark). Any change in the shape, size, or color of a mole may indicate melanoma. Melanoma usually looks like a flat, brown or black mole that has irregular, uneven borders and is not symmetrical. Melanoma lesions may be 6 mm (0.2 in.) or larger. A melanoma may be lumpy or rounded, change color, become crusty, ooze, or bleed.

In rare cases, melanoma can start under the nails or on the soles of the feet, on the palms of the hands, or on the mucous membranes that line body cavities such as the mouth, the rectum, and the vagina.

Melanoma may be cured if caught and treated in its early stages when it affects only the skin. Surgical removal, or excision, of the melanoma is the most effective treatment. For melanomas that have spread to the lymph nodes, a medication called interferon may be used after surgery to increase the chance for cure.