Brain cancer. Coloured magnetic resonance imaging (MRI) scan of an axial section through a patient's head showing two secondary brain tumours (dark areas at centre and lower right). The front of the head is at top. These tumours have 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.