Lung cancer starts when cells of the lung become abnormal and begin to grow out of control. As more cancer cells develop, they can form into a tumor and spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
Types of lung cancer
The 2 main types of lung cancer are:
- Small cell lung cancer (SCLC), which is sometimes called oat cell cancer. About 10% to 15% of lung cancers are SCLC.
- Non-small cell lung cancer (NSCLC), which makes up about 80% to 85% of lung cancers. The 3 main types of NSCLC are adenocarcinoma, squamous cell carcinoma, and large cell carcinoma.
Small cell and non-small cell lung cancers are treated differently. The information here focuses on small cell lung cancer. See Lung Cancer (Non-Small Cell).for information about that type of lung cancer.
Other types of lung cancer and tumors
Lung carcinoid tumors: Less than 5% of lung tumors are carcinoid tumors of the lung. Most of these grow slowly. For more information about these tumors, see Lung Carcinoid Tumor.
Other lung tumors: Other types of lung cancer such as adenoid cystic carcinomas, lymphomas, and sarcomas, as well as benign lung tumors such as hamartomas are rare. These are treated differently from the more common lung cancers and are not discussed here.
Cancers that spread to the lungs: Cancers that start in other organs (such as the breast, pancreas, kidney, or skin) can sometimes spread (metastasize) to the lungs, but these are not lung cancers. For example, cancer that starts in the breast and spreads to the lungs is still breast cancer, not lung cancer. Treatment for metastatic cancer to the lungs is based on where it started (the primary cancer site).
About the lungs
Your lungs are 2 sponge-like organs in your chest. Your right lung has 3 sections, called lobes. Your left lung has 2 lobes. The left lung is smaller because your heart takes up more room on that side of the body.
When you breathe in, air enters through your mouth and nose and goes into your lungs through the trachea (windpipe). The trachea divides into tubes called the bronchi (singular, bronchus), which enter the lungs and divide into smaller branches called bronchioles. At the end of the bronchioles are tiny air sacs known as alveoli.
The alveoli absorb oxygen from the inhaled air into your blood and remove carbon dioxide from the blood. This leaves the body when you exhale. Taking in oxygen and getting rid of carbon dioxide are your lungs’ main functions.
Lung cancers typically start in the cells lining the bronchi and parts of the lung such as the bronchioles or alveoli.
A thin lining called the pleura surrounds the lungs. The pleura protects your lungs and helps them slide back and forth against the chest wall as they expand and contract during breathing.
Below the lungs, a thin, dome-shaped muscle called the diaphragm separates the chest from the abdomen. When you breathe, the diaphragm moves up and down, forcing air in and out of the lungs.
Last Revised: 05/16/2016