a spreading and frequently recurring cancer of specialized skin cells (melanocytes) that produce the protective skin-darkening pigment melanin. In the United States melanoma represents less than 5 percent of all cases of skin cancer, yet it is responsible for nearly three-quarters of all skin cancer deaths and is increasing in frequency. Unlike other skin growths, melanoma is always malignant.

Like all cancers, melanoma is caused by changes in a cell's DNA that alter the cell's ability to control its growth. The most common cause of DNA damage is ultraviolet radiation from sunlight. People vary in their susceptibility to melanoma. Whites are 20 times more likely to develop melanoma than are blacks. People who have fair skin or who freckle easily are particularly susceptible. Individuals with a large number of moles or with several very large moles are also at increased risk. A family history of melanoma increases the risk of developing this cancer.

The earliest symptoms of melanoma are often visual. Large or abnormally coloured moles (mole) on the surface of the skin are early indicators. Melanoma can be detected in its early stages by regular self-assessment of moles, using the ABCD system. ABCD stands for asymmetry, border, colour, and diameter. Moles that are asymmetrical, have irregular borders (edges) or colour, or are greater than 5–6 mm (about ¹/₄ inch) in diameter are suspect. Any mole that changes in size, shape, or colour should be examined by a physician immediately.

Following the identification of a potential melanoma, diagnosis is made by skin biopsy. A sample of the skin is examined under a microscope for signs of cancer growth and for measurement of the thickness of the growth. If melanoma is diagnosed, several treatment (therapeutics) options are available, depending on the severity or stage of the disease. Stage 0 through stage II melanomas are confined to the skin, and most of these can be cured by excision of the tumour, especially if caught early. Stage III melanoma has spread to nearby lymph nodes, and surgical removal of the cancerous nodes is required. Stage IV melanoma has spread beyond the regional lymph nodes to other tissues in the body and is extremely serious. No cure for stage IV melanoma is available, but disease progression may be delayed by surgery or chemotherapy. Unfortunately, the survival rate for stage IV melanoma is extremely low.

The risk of melanoma is greatly reduced by avoiding exposure to ultraviolet light (ultraviolet radiation). Exposure can be reduced by staying out of direct sunlight during periods of peak intensity (11:00 AM to 3:00 PM), protecting the skin with clothing, or using a sunscreen with an SPF rating of 15 or higher. Children should be particularly careful to avoid sunburns, as an increased risk of developing melanoma has been linked to severe sunburns during childhood.