Lung cancer is often linked in people’s minds with smoking. In fact, most cases of lung cancer—about 80 percent—are related to tobacco use. But lung cancer can also develop in people who haven’t smoked.
What Is Lung Cancer?
Lung cancer is cancer that begins in the lungs. (Cancer that begins somewhere else in the body may spread to the lungs; this is different from lung cancer.) It occurs when cells in the lungs begin to grow abnormally. Cancer cells do not respond to regular cell growth, division, and death signals like healthy cells do. They also don’t organize normally. Instead they grow into a tumor, which may invade surrounding layers of tissue and possibly spread to other organs.
Lung cancer can start in the cells lining the bronchi (the two main airways that branch off the trachea, or windpipe) or within the lungs—in the bronchioles (smaller branches) or alveoli (air sacs). It often takes years to develop.
The cancer cells can enter the lymph system and begin to grow in lymph nodes around the bronchi and in the mediastinum (area between the lungs). If lung cancer has reached the lymph nodes, it is likely to have spread to other parts of the body as well.
Understanding the Lungs and Lymph System
To understand lung cancer, it helps to know more about the lungs and lymph system.
The lungs are sponge-like organs that work with the ribs, chest muscles, and diaphragm muscle to move air in and out of your body, bringing in oxygen (fuel) when you inhale and getting rid of carbon dioxide (waste) when you exhale. Air travels down your trachea, through your bronchi and bronchioles, into your alveoli, and back out again.
Many tiny blood vessels run through the alveoli. The alveoli exchange oxygen for carbon dioxide through these tiny blood vessels, replenishing your bloodstream with oxygen, which is then carried to other parts of your body.
Each lung has sections called lobes. The right lung has three lobes and is slightly larger than the left. The left lung has two lobes and is smaller because the heart takes up room on that side of the body.
A thin membrane called the pleura covers the outside of each lung and lines the inside wall of the chest. This creates a sac called the pleural cavity. The pleural cavity normally contains a small amount of fluid that helps your lungs move smoothly in your chest when you breathe.
Around the lungs are lymphatic vessels, small tubes that carry lymph away from the lungs. Lymph is clear fluid that carries both waste products and immune system cells. In certain places along the lymphatic vessels there are lymph nodes—small, oval-shaped organs of the immune system. Lymphatic vessels link lymph nodes in the lungs to lymph nodes in the mediastinum.
How Common Is Lung Cancer?
Lung cancer is the most common cancer after skin cancer, and it is the leading cause of cancer death for both men and women. Each year, more Americans die of lung cancer than of breast, colorectal, ovarian, and prostate cancers combined. Lung cancer is more common in older people. It is rare in people younger than age 45. More than 65 percent of lung cancers are diagnosed in people age 65 or older.
According to the American Cancer Society, more than 228,000 new lung cancer cases will be diagnosed and about 160,000 deaths will result from lung cancer in the United States in 2013.