Lung cancer. Coloured X-ray of the left lung of a patient with lung cancer. There is a malignant (cancerous) tumour (orange and purple) at the hilum of the lung (green). A hilum is an area through which blood vessels, nerves and ducts enter and leave an organ. This is an early stage of lung cancer, the main cause of which is cigarette smoking. Symptoms include chest pain, shortness of breath and a cough. Treatment is with a combination of chemotherapy and radiotherapy.