Lung Cancer; Overview.
In 2006, there will be an estimated 174,470 new cases of lung cancer accounting for about 13 percent of all cancers: an estimated 92,700 cases will be diagnosed in men and 81,770 in women. There will be approximately 162,460 lung cancer deaths (73,140 in women, accounting for 28 percent of all cancer deaths, according to the American Cancer Society. The incidence of lung cancer in women as a whole has climbed at an alarming rate. Since 1950, the lung cancer mortality rate for American women has increased about 600 percent. These increases are clearly attributable to the increases in the number of women who have smoked.
Lung cancer occurs most often in people over 50 who have a long history of cigarette smoking. Normal lung tissue is made up of cells programmed by genes to create tissue in a certain shape and to perform certain functions. Lung cancer develops when the genetic material responsible for the production of these cells is damaged, or mutates. Repeated exposure to carcinogens, such as tobacco smoke, causes the mutations. This damage is known as genetic mutation.
Mutations in the genetic material of the lung cells cause the instructions for those cells to go awry. Consequently, those cells and their offspring reproduce at a dramatic pace without regard for the normal shape and function of the lung. That wild reproduction causes the formation of tumors that may block air passages in the lung and prevent it from functioning as it should. Mutations may also prevent normal programmed cell death, in which cells commit a kind of "suicide," because they're abnormal, thus adding to the accumulation of cells and tumor formation.
Some genes are known as tumor suppressors. Their job is to keep abnormal cells from growing and forming tumors. Researchers have determined that a tumor suppressor gene called p53 is almost always defective in cases of small-cell lung cancer and in approximately half of non-small-cell lung cancer cases. Because of this genetic defect, p53 doesn't stop the reproduction of tumor cells as it should.
Some women inherit genes from their parents that are more resistant to damage and cancer than others. Those whose genes do not provide as much protection against cancer are said to be genetically susceptible to the disease. Scientists have shown that some cancers (i.e., breast cancer) involve genes that are passed down from parents to their children, and the link between such genetic mutations and lung cancer is also becoming more probable. But the link to heredity has not been absolutely confirmed in lung cancer.
Beyond genetic mutations, we know that smoking is the number one cause of lung cancer--87 percent of lung cancers are thought to be the result of smoking, according to the American Cancer Society. Cigarette smoke contains more than 4,000 different chemicals, 60 of which are proven carcinogens, and hundreds of others increase the cancer-causing power of carcinogens.
The more you smoke and the longer you smoke, the greater your risk of lung cancer. But if you stop smoking, the risk decreases steadily each year as abnormal cells are replaced by normal ones. However, the risk never completely returns to the same risk as people who never smoked. Since smoking cessation efforts in the U.S. have been reasonably successful, lung cancer has become, in large measure, a disease of former smokers.
The second most common risk factor for lung cancer in the U.S. is exposure to radon, particularly when combined with cigarette smoking. Radon is a radioactive gas found in the earth's rocks and soil. It is formed by the natural breakdown of radium, which is a radioactive product of decaying uranium. Radon problems have been identified in every state. This invisible, odorless gas can enter homes from the soil under foundations. Lung cancer risk increases when radon levels are present at high levels in the home and exposure occurs over a long period of time, according to the American Cancer Society. You can measure the radon level in your home with a test kit available in hardware stores. You can also hire a company to come to your home to check radon levels. The testing should be conducted more than once, with the results averaged together.
Another leading cause of lung cancer is on-the-job exposure to carcinogens. Asbestos is perhaps the best known industrial substance associated with lung cancer, but there are many cancer-causing substances that people may deal with at work. Others include uranium, arsenic and certain petroleum products.
Lung cancer takes years to develop. After exposure to carcinogens, a few unusual cells begin to develop. With continued exposure, more abnormal cells appear. These cells may be on their way to becoming cancerous and forming a tumor.
Lung tumors almost always start in the spongy, pinkish gray walls of the bronchi--the tubular, branching airways of the lungs. Although there are numerous types of malignant tumors that originate in the lung itself (primary lung cancer), the two major types are small-cell lung cancer and non-small-cell lung cancer.
Non-small-cell lung cancer has four sub-varieties:
Adenocarcinoma. The most common type of lung cancer, adenocarcinoma tends to originate along the outer edges of the lungs in the small bronchi or smaller bronchioles. It often spreads to the pleura, the lining of the lungs, a location that makes early detection difficult. Adenocarcinoma often presents as a metastasis (site of cancer spread) in the brain or bone even before any lung-related symptoms occur.
Bronchoalveolar carcinoma (BAC) is a subset of adenocarcinoma and tends to occur in multiple locations in the lung over time. It may initially be confused with pneumonia that fails to improve with treatment. It is the least common form of lung cancer.
Squamous cell carcinoma usually starts in cells of the central bronchi, the largest branches of the bronchial tree. It is the easiest to detect early, since its distinctive cells are likely to show up in tests of sputum samples. It also tends to be most curable if found early because it spreads relatively slowly.
Large-cell carcinomas are a group of cancers with large, abnormal-looking cells that may appear in any part of the lung.
Small-cell lung cancer comprises about 15 to 20 percent of lung cancers, and is the most aggressive form of the disease. Like squamous cell carcinoma, this cancer usually originates in the central bronchi. It spreads quickly, often before symptoms appear, making it particularly threatening. It frequently spreads (metastasizes) to the liver, bone and brain. Although usually very responsive to chemotherapy, small-cell lung cancer is less curable than other types because it usually isn't discovered until it has spread.
The symptoms of lung cancer vary, depending on several factors, including where in the lung the tumor is located. If the cancer is located in one of the bronchi, it can irritate the lining of the bronchus (one of the main airways that branches off of the trachea or windpipe) and cause a chronic cough. The cancerous area may bleed when a person coughs.
If the tumor grows larger, it may gradually fill the bronchus so air can't pass in or out. A blocked bronchus may also cause repeated lung infections or pneumonia.
A tumor located in the outer part of the lung may not produce any symptoms until it is fairly large. Sometimes the first sign may be chest pain from the tumor growing into the lining of the lung or the ribs and muscle of the chest wall. If the pleura, or lining of the lung, is involved, it often produces fluid, called a pleural effusion. This leads to shortness of breath because the fluid prevents the lung from expanding during breathing. Tumors that develop at the very top of the lung may irritate the nerves that supply the arm and cause severe pain or numbness in the arm. This is known as a superior sulcus, or Pancoast, tumor.
A person's lungs have extensive networks of blood and lymph vessels. Cancer cells may grow into these vessels and be carried by the blood or lymph to circulate through the body. The cancer cells may then be deposited in other organs of the body. A new colony of cancer cells, which starts in another organ, is known as a metastasis.
The first site of tumor metastasis is usually the lymph nodes within the lungs and the mediastinum (the space between the two lungs in the middle of the chest). Lymph nodes are small, bean-shaped structures found throughout the body. They produce and store infection-fighting cells.
It is possible for cancer cells that begin in other organs to spread to the lungs. These cases are very different medical problems, however. Depending on the organ of origin, such cases might be termed "primary breast cancer, metastatic to the lungs," or "primary kidney cancer, metastatic to the lungs."
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Keywords: lung cancer, cancer, breast cancer, women, smoking, cigarette, smoke, tumor, tumors, carcinogens, radon, radon levels, adenocarcinoma, pneumonia, metastasis, lymph nodes
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|Publication:||NWHRC Health Center - Lung Cancer|
|Date:||Sep 8, 2006|
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