Brain cancer. Coloured magnetic resonance imaging (MRI) scan of an axial section through a patient's brain showing a secondary brain tumour (black area, upper left). The front of the brain is at top. This tumour has spread (metastasised) from a malignant melanoma, a form of skin cancer. Malignant melanomas arise from cells (melanocytes) in the skin that produce the pigment melanin. The risk of developing melanoma is increased by excessive exposure to sunlight. Malignant melanomas invade and destroy surrounding tissues and often spread. Treatment is by excision of the primary tumour, with radiotherapy and chemotherapy if the cancer has spread.