MedGen

The occurrence of an immune reaction against the organism's own cells or tissues. [from HPO]

Melanoma is a type of skin cancer that begins in pigment-producing cells called melanocytes. This cancer typically occurs in areas that are only occasionally sun-exposed; tumors are most commonly found on the back in men and on the legs in women. Melanoma usually occurs on the skin (cutaneous melanoma), but in about 5 percent of cases it develops in melanocytes in other tissues, including the eyes (uveal melanoma) or mucous membranes that line the body's cavities, such as the moist lining of the mouth (mucosal melanoma). Melanoma can develop at any age, but it most frequently occurs in people in their fifties to seventies and is becoming more common in teenagers and young adults.

Melanoma may develop from an existing mole or other normal skin growth that becomes cancerous (malignant); however, many melanomas are new growths. Melanomas often have ragged edges and an irregular shape. They can range from a few millimeters to several centimeters across. They can also be a variety of colors: brown, black, red, pink, blue, or white.

Most melanomas affect only the outermost layer of skin (the epidermis). If a melanoma becomes thicker and involves multiple layers of skin, it can spread to other parts of the body (metastasize).

A large number of moles or other pigmented skin growths on the body, generally more than 25, is associated with an increased risk of developing melanoma. Melanoma is also a common feature of genetic syndromes affecting the skin such as xeroderma pigmentosum. Additionally, individuals who have previously had melanoma are nearly nine times more likely than the general population to develop melanoma again. It is estimated that about 90 percent of individuals with melanoma survive at least 5 years after being diagnosed. [from MedlinePlus Genetics]