What is lung cancer?
Lung cancer is the uncontrolled growth of abnormal cells originating within the lungs, usually in the layers of cells that line the air passages. These abnormal cells do not go through the natural stages of growth, division, and dying that normal cells do. They replicate unchecked, often forming one or more masses of cells (tumors). Tumors can damage healthy tissue and grow large enough to interfere with breathing. Lung cancer can eventually spread (metastasize) beyond the lungs into nearby lymph nodes, tissues, and other organs.
The lungs are part of the respiratory (breathing) system and are located in the chest, inside the rib cage and above the diaphragm. When a person inhales, air enters the lungs and flows through passages of decreasing diameter called bronchi and bronchioles. These passages carry oxygen to small sacs (alveoli) deep within the lung, where oxygen moves from the lung into the bloodstream, and carbon dioxide, a byproduct of metabolism, moves from the blood into the lung to be exhaled. Any lung disease that interferes with this exchange process, including lung cancer, can limit the amount of oxygen available and affect tissues and organs throughout the body.
According to the American Cancer Society (ACS), lung cancer is the second most common cancer in both men and women (other than skin cancer) and it is the leading cause of cancer death. More people die of lung cancer each year than of breast, prostate, and colon cancer combined. The ACS estimates that in 2013 there will be about 228,000 new cases of lung cancer in the U.S. and as many as 159,000 people will die of the disease. While anyone can get lung cancer, about 2 out of 3 new cases will be in people 65 years of age or older.
Risk factors for developing lung cancer include:
- Smoking – at least 80% of lung cancer deaths are thought to be related to smoking. The more a person smokes, and the longer that he or she smokes, the greater the risk. Second-hand smoke also increases risk of lung cancer.
- Radon exposure – a common cause of lung cancer in nonsmokers; it is a colorless, odorless radioactive gas that occurs naturally in soil but can accumulate in some homes.
- Asbestos exposure – this can increase the risk of lung cancer. Asbestos is more commonly associated with mesothelioma, a rare cancer of the lining of the chest and abdomen. Most cases of mesothelioma – about 70% to 80% – arise in people with a history of working with asbestos, especially in the shipbuilding, construction, automotive, and fireproofing industries.
- Exposure to cancer-causing substances (carcinogens) such as arsenic or chromium (often in the workplace)
- Radiation therapy – such as previous treatment for another type of cancer
- Family or personal history of lung cancer
Lung cancer begins in one of the cell types that exist in the lungs. Most cases are thought to be due to an acquired genetic change or mutation in DNA that leads to the production of an abnormal protein that either promotes the uncontrolled growth of cells or inhibits their natural death.
Cancer that spreads from another part of the body to the lungs, such as metastatic breast cancer, is not considered lung cancer. Cancers that have spread to the lungs from other areas are treated differently so they are not covered in this article.
There are two main categories of lung cancer, non-small cell and small cell. These cancers are named and differentiated based upon the size, shape, and characteristics of the tumor cells. In addition, there are several less common types of cancer that can affect the lungs. See the next page of this article for more on the types of lung cancers.