Brain tumour. Light micrograph of a section of a secondary brain tumour, caused by the spread (metastasis) of a skin cancer (malignant melanoma) to brain tissue. The cancer cells are black due to the melanin pigment they produce. The main risk factor for malignant melanoma is exposure to ultraviolet (UV) light from the sun or sunbeds. It may rarely be the result of an inherited gene defect. Metastasis to the central nervous system occurs in about a quarter of cancer cases. Aside from melanoma, types which often spread to the brain include kidney, liver and lung cancer. Treatment is usually surgery, radiation or a combination of the two. Magnification unknown.