Melanoma is a disease in which malignant (cancer) cells form in the skin cells called melanocytes (cells that color the skin). Melanocytes are found throughout the lower part of the epidermis. They make melanin, the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes make more pigment, causing the skin to tan, or darken. The skin is the body’s largest organ. It protects against heat, sunlight, injury, and infection. The skin has two main