Cancer is a disease in which cells grow in an abnormal way. Normally, the cells divide in a controlled manner to replace old or damaged cells. If cells keep dividing when new cells are not needed, a mass of tissue called a tumor forms.
Not all tumors are cancer, those that are cancer are called malignant. Cancer tumors invade and damage tissue around them. The cancer cells can also enter the lymph and blood streams, spreading to other parts of the body. Lung cancer is the development of malignant cells from lung tissue.
The lungs are two football-sized organs located in the chest cavity. Each lung is divided into sections called lobes. The left lung has 2 lobes and the right lung has 3 lobes. The lungs are surrounded by a membrane called the pleura. The inside layer of the pleura covers the lungs and helps separate the lobes. The outside layer is attached to the chest wall. The fluid that fills the space between the layers serves as a lubricant that allows the lungs to expand and contract in smooth movements. Cancer can develop in any of these areas.
Air moves through the nose or mouth enters the trachea, or windpipe. The trachea divides into tubes called bronchi, which lead into each lung. The bronchi further divide into smaller bronchioles, much like the branches on a tree. The bronchioles end in little air sacs called alveoli. Oxygen from the air passes to the blood through these air sacs. At the same time, carbon dioxide (a waste product) moves from the blood to the lungs so it can be exhaled from the body.
Cell division and growth is a normal process in the body to replace old or damaged cells. The inside of the lungs have a higher rate of cell turnover than other areas because of constant usage during normal breathing. Breathing also exposes the lungs to carcinogens (cancer-causing agents) from smoking, pollutants, and other chemicals in the air. These changes may irritate the cells and increase turnover from old to new cells.
Lung cancer can start anywhere in the respiratory tract, but it is most commonly found in the cells that form the lining of the bronchi or alveoli. Tumors that grow in the lungs can cause a persistent, worsening cough or shortness of breath. If it grows beyond the lungs, the cancer can penetrate nearby structures, such as the great blood vessels that lead to and from the heart, tissue in and around the heart, or major nerves. The cancer can also spread to the lymph nodes or blood vessels, which can carry cancer cells to other areas of the body. The most common sites for lung cancer to spread to are the lymph nodes in other parts of the body, the liver, bones, or brain.
Lung cancer is categorized by where tumors start, how they grow, and their appearance under a microscope. Lung cancer types include:
Many types of metastatic cancers in other parts of the body spread to the lungs. This fact sheet focuses on non-small cell and small cell cancers that start in the airways and/or lungs.
Carcinoid tumors. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T114031/Carcinoid-tumors. Updated July 18, 2017. Accessed August 30, 2017.
Lung cancer basics. American Lung Association website. Available at: http://www.lung.org/lung-health-and-diseases/lung-disease-lookup/lung-cancer/learn-about-lung-cancer/what-is-lung-cancer/lung-cancer-basics.html. Updated November 3, 2016. Accessed August 30, 2017.
Non-small cell lung cancer. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T114774/Non-small-cell-lung-cancer. Updated June 23, 2017. Accessed August 30, 2017.
Non-small cell lung cancer. National Cancer Institute website. Available at: https://www.cancer.gov/types/lung/patient/non-small-cell-lung-treatment-pdq. Updated April 13, 2017. Accessed August 30, 2017.
Small cell lung cancer. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T115654/Small-cell-lung-cancer. Updated June 23, 2017. Accessed August 30, 2017.
Small cell lung cancer. National Cancer Institute website. Available at: https://www.cancer.gov/types/lung/hp/small-cell-lung-treatment-pdq. Updated January 20, 2017. Accessed August 30, 2017.
What is non-small cell lung cancer? American Cancer Society website. Available at: https://www.cancer.org/cancer/non-small-cell-lung-cancer/about/what-is-non-small-cell-lung-cancer.html. Updated May 16, 2016. Accessed August 30, 2017.
What is small cell lung cancer? American Cancer Society website. Available at: https://www.cancer.org/cancer/small-cell-lung-cancer/about/what-is-small-cell-lung-cancer.html. Updated May 16, 2016. Accessed August 30, 2017.
Last reviewed August 2017 by EBSCO Medical Review Board Michael Woods, MD, FAAP
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