Skin cancer cell, colored scanning electron micrograph (SEM). Skin cancer arises from the skin's melanocytes, the cells that produce the pigment melanin which gives skin its color. Melanoma is an aggressive cancer that often spreads (metastasizes) to other tissues of the body. This sample came from the skin of the forearm of an 83 year old woman. The main cause of melanoma is exposure to ultraviolet radiation in sunlight. Magnification: x1200 when printed at 10 centimeters wide.