Melanoma is a cancer characterized by the uncontrolled growth of pigment-producing cells called melanocytes. Melanocytes are present in the epidermis, or outermost layer of the skin. The cancer sometimes develops from moles, but can appear spontaneously. Other facts:

Melanoma can appear anywhere, but most often develops on the upper back in men and on the legs in women.

Excessive exposure to sunlight is the greatest preventable risk factor for melanoma and other skin cancers.

Sources: The American Cancer Society; the American Academy of Dermatology