Lung cancer. Coloured computed tomography scan of a patient's chest showing a malignant tumour (red) in the lung on the left. The black areas in the chest represent normal lung tissue. The large red structure between the lungs is the heart. Lung cancer is one of the most common and dangerous forms of cancer. Fewer than 10% of patients survive for five years after diagnosis. The main cause is cigarette smoking. Secondary lung cancer, resulting from spread of cancer cells from elsewhere in the body, is also a common cause. Treatment includes surgical removal of all or part of the lung, anti-cancer drugs and radiotherapy.