Lung Cancer — What Is It? Classified as small cell and non-small cell, lung cancer is the leading cause of cancer death. Learn how it develops and spreads. Lung cancer is the leading cause of cancer death for both men and women. More people die of lung cancer than of colon, breast, and prostate cancers combined. Lung cancer is rare in people under the age of 45. The American Cancer Society's most recent estimates for lung cancer in the United States are for 2010: - 222,520 new cases of lung cancer (both small cell and non-small cell) - 157,300 deaths from lung cancer The average lifetime chance that a man will develop lung cancer is about 1 in 13. For a woman it is 1 in 16. These numbers include both smokers and non-smokers. For smokers the risk is much higher, while for non-smokers the risk is lower. Understanding Lung Cancer To understand lung cancer, it helps to know about the normal structure and function of the lungs. The lungs are two sponge-like organs found in the chest. The right lung has three sections, called lobes. The left lung has two lobes, as shown in the picture below. The left lung is smaller because the heart takes up more room on that side of the body. The lungs bring air in and out of the body. They take in oxygen and get rid of carbon dioxide gas, a waste product. The lining around the lungs, called the pleura, helps to protect the lungs and allows them to move during breathing. The windpipe (trachea) brings air down into the lungs. It divides into tubes called bronchi (singular, bronchus) which divide into smaller branches called bronchioles. At the end of these small branches are tiny air sacs known as alveoli. Most lung cancer starts in the lining of the bronchi, but it can also start in other parts of the lung. Lung cancer often takes many years to develop. First, there may be areas of pre-cancerous changes in the lung. These changes are not a mass or tumor. They can't be seen on an X-ray and they don't cause symptoms. Over time, these pre-cancerous areas may go on to become cancer. The cancer makes chemicals that cause new blood vessels to form nearby. These new blood vessels feed the cancer cells and allow a tumor to form. In time, the tumor becomes large enough to show up on an X-ray. At some point, cancer cells can break away and spread to other parts of the body in a process called metastasis. Lung cancer is a life-threatening disease because it often spreads in this way before it is found. The Spread of Lung Cancer One of the ways lung cancer can spread is through the lymph system. Lymph vessels are like veins, but they carry lymph fluid instead of blood. Lymph is a clear fluid that contains tissue waste products and cells that fight infection. Lung cancer cells can enter lymph vessels and begin to grow in lymph nodes around the bronchi and in the area between the lungs. When lung cancer cells have reached the lymph nodes, they are more likely to have spread to other organs of the body. Staging and decisions about lung cancer treatment are based on whether or not the cancer has spread to the nearby lymph nodes. Types of Lung Cancer There are two main types of lung cancer — small cell lung cancer and non-small cell lung cancer — and they are treated differently. If the cancer has features of both types, it is called mixed small cell/large cell cancer. Non-small cell lung cancer: About 8 to 9 out of 10 cases of all lung cancers are the non- small cell type. There are three subtypes of. The cells in these sub-types differ in size, shape, and chemical makeup. Squamous cell carcinoma: About 25 percent to 30 percent of all lung cancers are this kind. It is linked to smoking and tends to be found in the middle of the lungs, near a bronchus. Adenocarcinoma: This type accounts for about 40 percent of lung cancers. It is usually found in the outer part of the lung. Large-cell (undifferentiated) carcinoma: About 10 percent to 15 percent of lung cancers are this type. It can start in any part of the lung. It tends to grow and spread quickly, which makes it harder to treat. Small cell lung cancer: About 10 percent to15 percent of all lung cancers are the small cell type. Other names for it are oat cell carcinoma and small cell undifferentiated carcinoma. This type of cancer is almost always caused by smoking. It is very rare for someone who has never smoked to have small cell lung cancer. Small cell lung cancer often starts in the bronchi near the center of the chest. Although the cancer cells are small, they can multiply quickly and form large tumors that can spread throughout the body. This is important because it means that surgery is rarely an option and never the only treatment given. Treatment must include drugs to kill the widespread disease. Along with the two main types of lung cancer, other tumors can be found in the lungs, too. Some of these are not cancer and others are cancer. Carcinoid tumors, for instance, are slow-growing and usually cured by surgery. Keep in mind that cancer that starts in other organs (such as the breast, pancreas, kidney, or skin) and spreads (metastasizes) to the lungs is not the same as lung cancer. For example, cancer that starts in the breast and spreads to the lungs is still breast cancer, not lung cancer. Treatment for these cancers that have spread to the lungs depends on where the cancer started.
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