Skin cancer cell. Coloured scanning electron micrograph SEM of a melanoma cancer cell. This cancer arises from the skin磗 melanocytes, the cells that produce the pigment melanin that give skin its colour. Melanoma is an aggressive cancer that often spreads metastasises to other tissues of the body. Once the cancer has spread the prognosis is poor. The long irregular cell surface is typical of cancer cells. The main cause of melanoma is exposure to ultraviolet radiation in sunlight.