Metastatic malignant melanomas on the skin of a 62 year old man. The melanomas have spread (metastasised) from a primary lesion that has been removed (scar at top). Melanoma is a form of skin cancer that arises from melanocytes, the cells that produce melanin, the pigment that gives skin its colour. The main cause of melanoma is exposure to ultraviolet radiation in sunlight. It is an aggressive cancer that often spreads to other parts of the body. If this occurs, the prognosis is poor. Treatment is with surgical excision of the melanoma.