All skin cancers originate in the outer layer of skin known as the epidermis.
Melanoma is cancer of melanocytes , cells that produce a protective pigment called melanin . It can start in heavily pigmented tissue, such as a mole or birth mark, as well as in normally pigmented skin. Skin cancer is by far the most common cancer in the world. Most cases are cured, but the disease is a major health concern because it affects so many people. Over 700,000 cases of nonmelanoma skin cancers are diagnosed annually in the United States alone, and about 32,000 cases of melanoma.