Lung cancer is a disease marked by the uncontrolled growth of abnormal cells in the lungs. The abnormal cells may no longer do the work of normal cells, and they crowd out and destroy healthy tissue. Lung cancer is the most common cancer-related cause of death among men and women, and it is the second most commonly occurring cancer among men and women.
There are two major types of cancers that begin in the lungs -- non-small cell lung cancer and small cell lung cancer. Non-small cell lung cancer, which includes squamous cell carcinoma, adenocarcinoma and large cell carcinoma, generally spreads to distant organs more slowly than small cell lung cancer. Small cell lung cancer, or oat cell cancer, is less common and accounts for about 20 percent of all lung cancer. It is important to find out what kind of lung cancer a person has because the different types of carcinomas involve different regions of the lung, which as a result may cause different symptoms and may need to be treated differently.
Lung cancer occurs in people who have exposed to carcinogens (cancer-causing substances). While it usually takes many years for lung cancer to develop, changes in the lung begin almost immediately once someone is exposed. Once there has been exposure to carcinogens, unusual cells may appear on the tissue lining the bronchi, which are the main breathing tubes. If there is continued exposure, more abnormal cells can appear and may become cancerous and form a tumor.
There are many types of carcinogens that can cause lung cancer, but carcinogens in cigarettes seem to be the biggest cause. Cigarette smoke contains more than 4,000 different chemicals, many of which are proven carcinogens, while hundreds of others increase the cancer-causing power of carcinogens. Studies show that more than 80 percent of lung cancers result from smoking. Another leading cause of lung cancer is exposure to carcinogens while working in different industries. Asbestos is perhaps the best known of the industrial substances associated with lung cancer, but there are many cancer-causing substances that people may deal with at work, including uranium, arsenic, certain petroleum products and others.
Lung cancer has a variety of symptoms, but they usually vary depending upon the tumor's location and size and other factors. Some symptoms include chronic cough, lung infections or pneumonia and chest pain. A person may have a cough if the cancer is located in one of the bronchi, which would cause irritation in the lining of the bronchus (one of the main airways that branches off of the trachea or windpipe). If the tumor grows larger, it may gradually fill the bronchus so that air can't pass in or out. A blocked bronchus may also cause repeated lung infections or pneumonia. A tumor that is located in the outer part of the lung may not produce any symptoms until it is fairly large. A person's first sign of lung cancer may be chest pain from the tumor growing into the lining of the lungs or the ribs and muscle of the chest wall.
