Smoking is the main risk factor for lung cancer and is responsible for more than 80% of lung cancers. The longer you have smoked and the more you smoke, the more likely you are to get lung cancer. If you stop smoking before cancer cells develop, lung tissue that has been damaged by smoking will start to repair. An ex-smoker's risk will not be as low as that of a person who never smoked, but over time, their risk will go down. Cigar smoking and pipe smoking are almost as likely to cause lung cancer as cigarette smoking.

Even secondhand smoke, the kind inhaled from nearby smokers, can cause lung cancer. Nonsmokers who are married to smokers have a 30% greater risk of developing lung cancer than spouses of nonsmokers.

Living in an environment with high air pollution or working with radioactive minerals or asbestos can also increase the risk of cancer. Research has helped us to understand how these risk factors produce certain changes in the DNA of lung cells. These changes cause the cells to grow abnormally and form cancers.

DNA is the genetic material that carries the instructions for nearly everything our cells do. Some genes (parts of our DNA) contain instructions for controlling when cells grow and divide. The risk factors discussed earlier can trigger changes, also called mutations, in these genes that result in cancer. A risk for some types of cancer (e.g., breast, ovarian, colorectal, and several others) can be inherited from parents. However, inherited gene mutations are not thought to be a cause of very many lung cancers.

The first and most common symptom of lung cancer is a cough. If someone with chronic bronchitis develops lung cancer, the cough due to bronchitis will get worse. Cancer may grow into the blood vessels and cause blood to be coughed up in the phlegm. It may also grow into or press on the bronchi, making them narrower and causing the patient to wheeze when trying to breathe. Cancer can grow into the chest wall, causing chest pain. It can also cause pneumonia, with its symptoms of cough, fever, chest pain, and shortness of breath. People with advanced lung cancers lose their appetite, feel weak, and lose weight.

Lung cancer can spread to parts of the body near the lungs or to other parts of the body such as the liver, brain, and bones, causing pain. It can also grow into and block the veins that go from the upper part of the body to the heart. This syndrome, called superior vena cava syndrome, causes the blood in the veins of the face, neck, and upper chest to back up and the veins to swell.

Cancer can cause fluid to fill the sacs surrounding the heart or lung, making it very hard to breathe. Cancerous cells can also press on the lung, causing it to collapse, or on the spinal cord (backbone), causing pain or the loss of function of the nerves. Some cancers also release hormones that can affect the body's metabolism.

Lung cancer is usually suspected when a chest X-ray shows a shadow on the lung. To confirm the diagnosis, a doctor will examine phlegm or mucus that is coughed up. A lesion found on a chest X-ray can be confirmed by a CT scan of the chest and a long needle can be placed through the chest under CT guidance to biopsy (take a sample of) the lesion.

Doctors will usually examine the lungs through a viewing instrument inserted into the bronchi. This procedure is called a bronchoscopy. A biopsy may also be done during the bronchoscopy.

During a biopsy, a sample of abnormal tissue is removed from the lung and later inspected with a microscope. Tissue for a biopsy may also be surgically removed by opening the chest.

Lung cancer can be managed with surgery, radiation therapy, and chemotherapy, either alone or in combination, depending on how advanced the tumour has developed. Which treatment or combination of treatment that is best will depend on the type of lung cancer, how advanced the cancer is (i.e., the stage of the cancer), overall health, side effects, and the potential for curing the cancer, relieving symptoms, or prolonging life.

Surgery can only be done if the cancerous tumour is small and localized to one lung, and if the remaining lung is strong enough to work on its own. The surgery is called a pneumonectomy if the whole lung is removed, or a lobectomy if only part of the lung is removed. The doctor decides how much of the lung to remove during the surgery. Although 10% to 35% of lung cancers can be surgically removed, surgery doesn't always cure the cancer. Surgery is only recommended for people in good enough health with no sign of metastatic spread of the tumour. If a person has a serious heart or other lung condition, surgery may not be an option.

Radiation is used for lung cancer that has spread or is too close to the windpipe. For people with serious disease, radiation is used to keep the cancer from growing, rather than to destroy it entirely. Radiation can control bone pain, superior vena cava syndrome and compression of the nerves to the backbone (spinal cord) caused by cancerous cell growth.

Chemotherapy, which is treatment with anticancer medications, may be used to prolong life when lung cancer is metastatic (spread to other areas of the body), or chemotherapy in combination with radiation may be used to control lung cancer that is still contained within the chest. Recently, molecularly targeted therapy has been found to extend survival rates in some patients with metastatic cancer.

The highest chance for a cure is in those people where the lung cancer was found and surgically removed or treated in its early stages. The estimated 5-year survival rate for all stages of lung cancer is about 20%. However, if the cancer has spread outside of the chest, it's not usually curable.

It's important for people who have had lung cancer to have regular checkups. Some people who have had lung cancer surgically removed will get it again. The figure is even higher for those who keep smoking after the surgery. Prevention of lung cancer is possible; deciding to quit smoking is the first big step. There are many helpful techniques and treatments for smoking cessation; see our article on this topic.

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