Mesothelioma. Coloured computed tomography (CT) scan of an axial section through the chest, showing mesothelioma cancer in the pleural lining of a lung. Mesothelioma is commonly caused by the inhalation of asbestos dust. Here, the tumour is taking up a large area of the lung field (at left, blue) which should be clear and black. A normal lung field is at right. The heart is seen at upper centre. White rib bones are seen around the chest. Mesothelioma may be symptomless or may cause coughs, chest pain and breathing difficulties. This form of cancer often spreads out quickly over the pleura, making it difficult to treat.