text: LUNG CANCER\nLung cancer is a malignant tumour of the lungs. Most commonly it is bronchogenic carcinoma (about 90%). Lung cancer is the most lethal malignant tumour worldwide, causing up to 3 million deaths annually. Only one in ten patients diagnosed with this disease will survive the next five years. Although lung cancer was previously an illness that affected predominately men, the lung cancer rate for women has been increasing in the last few decades, which has been attributed to the rising ratio of female to male smokers.\n\n \nThe incidence of lung cancer is highly correlated with smoking. The above is an illustration for the United States incidence of lung cancer.Current research indicates that the factor with the greatest impact on risk of lung cancer is long-term exposure to inhaled carcinogens. The most common means of such exposure is tobacco smoke.\n\nTreatment and prognosis depend upon the histological type of cancer and the stage (degree of spread). Possible treatment modalities include surgery, chemotherapy\n\n\nSigns and symptoms\nSymptoms that suggest lung cancer include:\n\ndyspnea (shortness of breath) \nhemoptysis (coughing up blood) \nchronic cough \nwheezing \nchest pain \ncachexia (weight loss), fatigue and loss of appetite \ndysphonia (hoarse voice) \nclubbing of the fingernails (uncommon) \nIf the cancer grows into the lumen it may obstruct the airway, causing breathing difficulties. This can lead to accumulation of secretions behind the blockage, predisposing the patient to pneumonia.\n\nMany lung cancers have a rich blood supply. The surface of the cancer may be fragile, leading to bleeding from the cancer into the airway. This blood may subsequently be coughed up.\n\nDepending on the type of tumor, so-called paraneoplastic phenomena may initially attract attention to the disease. In lung cancer, this may be Lambert-Eaton myasthenic syndrome (muscle weakness due to auto-antibodies), hypercalcemia and SIADH. Tumors in the top (apex) of the lung, known as Pancoast tumors, may invade the local part of the sympathetic nervous system, leading to changed sweating patterns and eye muscle problems (a combination known as Horner's syndrome), as well as muscle weakness in the hands due to invasion of the brachial plexus.\n\nIn many patients, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention. Common sites of metastasis include the bone, such as the spine (causing back pain and occasionally spinal cord compression) and the brain.\n\nTypes\nThere are two main types of lung cancer categorised by the size and appearance of the malignant cells seen by a histopathologist under a microscope: small-cell (roughly 20%) and non-small cell (80%) lung cancer. This classification although based on simple pathomorphological criteria has very important implications for clinical management and prognosis of the disease.\n\n\nCauses\nExposure to carcinogens, such as those present in tobacco smoke, immediately causes cumulative changes to the tissue lining the bronchi of the lungs (the bronchial mucous membrane) and more tissue gets damaged until a tumour develops.\n\nThere are four major causes of lung cancer (and, actually, cancer in general):\n\nCarcinogens such as those in cigarette smoke \nRadiation exposure \nGenetic susceptibility \nViral infection \n\n\nThe role of smoking\nSmoking, particularly of cigarettes, is believed to be by far the main cause of lung cancer, which at least in theory makes it one of the easiest diseases to prevent. In the United States, smoking is estimated to account for 87% of lung cancer cases in the U.S. (90% in men and 79% in women). There are hundreds of known carcinogens—such as polynuclear aromatic hydrocarbons—present in cigarette smoke. The length of time a person continues to smoke as well as the amount smoked increases the person's chances of contracting lung cancer. If a person stops smoking, these chances steadil