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Although smoking can cause many different physical ailments, one of the most serious diseases associated with tobacco use is lung cancer. Smoking causes 87 percent of all cases of lung cancer. The leading cause of cancer deaths in America, lung cancer costs more people their lives than prostate, colon, lymph, and breast cancer combined.

The risk of lung cancer increases the longer you smoke, and the more cigarettes you smoke regularly. However, if you quit smoking?even after many years?you can still greatly reduce your risk of lung cancer. Prevention of the disease is very important because lung cancer typically is not found until it has reached an advanced stage. The survival rate for lung cancer victims, although improving, is still below that of many other cancers.

The most common symptom of lung cancer is usually a cough. This cough is caused by a tumor blocking passage of air or irritating the airway lining. Other symptoms include coughing up blood, chest pain, a ?smoker?s cough? that grows worse, repeated bouts of pneumonia or bronchitis, shortness of breath, fatigue, appetite and subsequent weight loss, or hoarseness lasting over two weeks. Sometimes, lung cancer spreads to other parts of the body (also called metastasizing), and may cause headaches or bone pain.

a) Background-
Human lungs are paired organs that occupy the majority of the chest cavity, located on either side of the heart. The left lung has two lobes and the right lung has three. The pleura, a thin membrane, cover the lungs. Likewise, airway and windpipe linings have surface cells (columnar epithelium) and glands that produce mucus and other fluids.

Air travels from the nose or mouth through the trachea, which separates into two bronchi that enter either lung. Within the lungs, the bronchi continue dividing into smaller tubules, the smallest of which is called the alveoli. Alveoli are grouped in clusters, or lobules, which are then grouped into lobes. An alveolus is surrounded by capillaries. Capillaries are part of the pulmonary blood vessels that connect the lungs to the heart. Blood flows through the capillaries, carbon dioxide is delivered into the alveoli, and oxygen is diffused in the bloodstream.

The columnar epithelium (airways and windpipe lining) in healthy lungs divide in an orderly, controlled manner. When a person has lung cancer, these cells continue to reproduce past the point when new cells are needed. Lung cancer may take years to develop, but lung tissue may start to change immediately after being exposed to carcinogens in cigarette smoke. Continued smoking means more exposure to carcinogens; normal cells become more damaged and may become cancerous. Because of the great reach of the lung?s cells throughout the body, cancerous cells may spread throughout the body (metastasize) more easily.

b) Lung Cancer Causes and Types-
As previously mentioned, cigarette smoking is the number one cause of lung cancer. Exposure to secondhand smoke, asbestos and other industrial carcinogens, and high concentrations of radon are other potential causes of lung cancer. In particular, smokers who experience exposure to asbestos or radon are even more at risk for cancer than nonsmokers.

A cancer is named by the body part in which it originated. So even if a nonsmoker has cancer in the kidney that spreads (metastasizes) to the lungs, it is considered metastatic kidney cancer. Nonsmokers rarely get lung cancer, and smoking does not affect the spread of cancer from other body parts to the lungs.

Of cancers originating in the lungs, there are two main types: small cell and non-small cell. Small cell cancer afflicts smokers almost exclusively, and spreads early on during the course of the disease. This type of cancer is typically treated with chemotherapy and radiation, as surgery is generally not an option. However, the five-year survival rate is very low.

More than 75 percent of lung cancers are non-small cell. The four main types of non-small cell cancer are squamous cell carcinoma, adenocarcinoma, large cell carcinoma, and bronchoaveolar carcinoma. If caught early in the course of the disease, non-small cell cancer can often be surgically removed. Adenocarcinoma is common for nonsmokers and people exposed to secondhand smoke. On the other hand, bronchoaveolar carcinoma tends to occur more often in smokers and in more than one location simultaneously.

c) Conclusion:
Causing nearly 90 percent of lung cancer cases, smoking is by far the greatest risk factor for this disease. However a decade after quitting, your risk of lung cancer is reduced by one-third. Reducing the number of cigarettes smoked can also reduce the risk, although it is not nearly as effective as quitting entirely.

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