Lung cancer is the most common cancer in the world, causing more than 1.3 million deaths annually. Most lung cancers occur in people who smoke, but the cancer does affect individuals who have never smoked.
Types and Causes of Lung Cancer
Almost all lung cancers fall into one of two types: non-small cell carcinomas, which comprise more than 80 percent of lung cancer cases, and small cell carcinomas, which account for about 17 percent of cases. Within each group there are smaller subtypes of lung cancer, but generally all of the cancers within each group are treated similarly. There are several risk factors that have been identified with an increased risk for the development of lung cancers, including:
- Smoking: About 90 percent of all lung cancers occur in individuals who smoke, as a result of the inhalation of several known carcinogenic (cancer-causing) chemicals and other agents. Smoking also depresses the immune system, which allows for tumors to grow and spread.
- Passive smoking: Exposure to smoke, either at home or in the workplace, can also increase an individual’s chances of developing lung cancer. Recent studies have indicated the non-filtered smoke inhaled from passive smoking contains more dangerous carcinogens than the filtered smoke inhaled through direct smoking.
- Radon exposure: Occurring naturally in rocks and soil, radon is a colorless and odorless gas that has been associated with an increased risk for lung cancer. Some regions throughout the world have higher radon levels than others.
- Asbestos exposure: In addition to causing mesothelioma, asbestos exposure can also increase the risk for developing lung cancer.
- Viruses: Certain viruses, such as human papillomavirus and cytomegalovirus, may cause an increased risk for lung cancer.
- Genetics: Researchers have identified gene characteristics that make some individuals more likely to develop lung cancer than others.
Lung Cancer Diagnosis
Lung cancer can cause many symptoms, including shortness of breath, wheezing, chronic coughing and chest pain. Many of these symptoms can initially be misdiagnosed as asthma, allergies or other illnesses affecting the airways. More serious or advanced cases may result in coughing of blood or weakness and fatigue, as well as loss of appetite and unintentional weight loss. The tool most often initially used to diagnose lung cancer is the chest x-ray. Other tools, such as a bronchoscopy or a computer tomography scan, may also be used to aid in diagnosis. In many cases, a biopsy – or small tissue sample – will be taken to confirm the diagnosis and help identify the type of lung cancer.