Lung cancer is a cancer normally found in smokers, but in areas where there is a lot of air pollution it is also present.
Lung cancer is the leading cause of cancer deaths, among both men and women. It claims more lives than colon, prostate and breast cancer combined.
Yet most of these deaths could have been prevented. That's because smoking accounts for about 85 percent to 90 percent of lung cancer cases. Although your risk of cancer increases with the length of time and number of cigarettes you smoke, quitting smoking, even after many years, can greatly reduce your chances of developing the disease.
Protecting yourself from exposure to other leading causes of lung cancer, such as asbestos, radon and secondhand smoke, also decreases your risk. Prevention is especially important because lung cancer usually isn't discovered until it's at an advanced stage when the outlook for recovery is less positive.
Treatment for lung cancer depends on the type of cancer, how advanced it is and your overall health. In some cases, surgical removal of the tumor may be an option. In others, chemotherapy, radiation or a combination of the two is likely to provide better results.
Signs and symptoms
Because lung cancer doesn't cause signs or symptoms in its earliest stages, it's often quite advanced by the time it's diagnosed. The most common warning sign is a cough, which occurs when a tumor irritates the lining of the airways or blocks the passage of air. In addition to a new cough, be alert for:
Lung cancer also may cause fatigue, loss of appetite and weight loss. If it has spread to other parts of your body (metastasized), you may have headaches or bone pain.
Although many of these symptoms might be attributed to other causes, talk to your doctor if you experience such problems. The earlier you discover and treat lung cancer, the better chance you have of lengthening your life and reducing symptoms.
Your lungs are two large, spongy organs shaped something like an upside-down butterfly. One lung is located on each side of your chest. They're separated by the mediastinum the tissues and organs of your mid chest, which include your heart, esophagus and windpipe (trachea) as well as lymph nodes and major blood vessels such as the aorta. Each lung is divided into upper and lower sections called lobes. Your left lung has two lobes, and your right lung, which is larger and heavier, has three lobes.
Every time you inhale, air is carried through the windpipe to your lungs in two major airways called bronchi. Inside your lungs, the bronchi subdivide nearly 20 times into a million smaller airways (bronchioles), which finally end in clusters of tiny air sacs called alveoli. Within the air sacs, oxygen is absorbed into your bloodstream and carbon dioxide a waste product of metabolism is released.
How cancer forms
These abnormal cells primarily originate when the lungs are exposed to cancer-causing substances (carcinogens), such as those found in cigarette smoke, radon and asbestos.
At first only a small number of abnormal cells (precancerous lesions) may appear, but with repeated exposure to carcinogens over a number of years, these cells may increase and eventually become cancerous (malignant). And because cells in your lungs have easy access to a large number of blood and lymph vessels, tumors may be carried to other sites within your body, even before you have any symptoms.
Cigarette smoking accounts for the great majority of all lung cancers. Tobacco smoke contains more than 3,500 chemicals, at least 40 of which are known carcinogens. Cigarettes also contain at least 30 toxic metals, including nickel and cadmium, as well as radioactive compounds such as polonium 210.
Other risk factors for lung cancer include exposure to secondhand smoke, to asbestos and other industrial carcinogens, and to high concentrations of radon an odorless gas that's released into the air from the breakdown of uranium in the soil and water. Smokers exposed to asbestos and radon are far more likely to develop cancer than are nonsmokers.
Primary lung cancer is uncommon in nonsmokers, but cancer of the breast, colon, prostate, testicle, kidney, thyroid, bone or other organs may spread to the lungs. In that case, however, the cancer is still referred to by the name of the organ in which it originated, rather than being called lung cancer.
Types of lung cancer
Non-small cell lung cancer, which is more common, accounts for almost 75 percent of lung cancers. If caught early when it's confined to a small area, it often can be removed surgically. There are three major categories of non-small cell lung cancer:
Smoking remains the greatest risk factor for lung cancer, accounting for as many as 9 out of every 10 cases of the disease. Your risk increases with the number of cigarettes you smoke each day and the number of years you have smoked. Your risk is also greater if you start smoking early in life even if you later quit. Smoking filtered, low-tar or low-nicotine tobacco offers no additional protection because most people who smoke these cigarettes inhale more deeply, which also increases the risk. The good news is that it's never too late to quit smoking. Quitting at any age can lower your risk of developing lung cancer.
Other risk factors include:
Screening and diagnosis
Screening for lung cancer is controversial. The American Cancer Society currently doesn't recommend screening tests for lung cancer, even in high-risk individuals. But some doctors believe that smokers, especially those 50 years or older, should have an annual chest X-ray, although having annual chest X-rays has never been shown to be of particular benefit.
Complicating matters further is a study that appeared in the March 2003 issue of Radiology. It found that a new type of computerized tomography (CT) scan might detect lung cancer at a much earlier stage in high-risk people than conventional CT scans do. But the type of imaging called a spiral CT scan also has serious drawbacks. In the study 1,049 of the 1,520 people screened had lumps called noncalcified lung nodules. These people needed to undergo the further expense, stress and including possible surgery of additional testing. Yet in more than 95 percent of cases, the nodules turned out not to be cancerous.
Canadian researchers think they may have found a way to reduce the number of unnecessary procedures that result from CT screening, however. Many long-time smokers who develop lung cancer have abnormal cells in their sputum. Performing a sputum analysis first may help decide just who is most likely to benefit from screening.
Non-small cell lung cancer
Small cell lung cancer
Your lungs are abundantly supplied with blood and lymph a fluid that helps return water and proteins from your tissues to your blood. Lung cancer spreads easily to other parts of your body through your bloodstream and lymph system.
Small cell cancer, in particular, is a fast-growing tumor that quickly spreads to other organs. At the time of diagnosis, this type of cancer has already spread in more than two-thirds of people with the condition. Without treatment, the tumor will continue to grow and may prove fatal within a matter of months.
This kind of cancer responds very well to chemotherapy and radiation therapy better than do non-small cell lung cancers. But even when there is a positive response to treatment, relapses usually occur within two years. Unfortunately, at that point the cancer usually isn't as responsive to further therapy.
In addition, some non-small cell lung cancers even those identified at any early stage may spread undetectably (micrometastasis) to lymph nodes and other organs. As a result, cancer can reappear months and even years after treatment.
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