All of the normal cells in your body have very specific jobs and functions. For example, intestine cells absorb vitamins, minerals and other nutrients from food; red blood cells carry oxygen throughout the body; and white blood cells fight infections. Normal cells stop growing and dividing when they get old. Normal cells also die if they are injured.
Cancer cells do not function normally; they continue to divide and multiply, and do not die when they are supposed to.
Every cell contains genes, which are the “brains” that tell the cell what to do. When a cell’s genes are mutated (damaged or changed) cancer may develop. Some of these changes are inherited (passed down from parent to child), but others may occur as a result of exposure to certain toxins, such as cigarette smoke, radon and asbestos. When these mutations in genes cause cells to multiply uncontrollably, a mass of cancer tissue, called a tumor, can develop.
Cancer cells can also spread through the blood stream to other organs or invade nearby lymph nodes (small collections of white blood cells scattered throughout the body) and spread through the lymph system. When cancer cells spread through any of these methods, they metastasize (travel to other organs and form new tumors).
Common lung cancer metastasis sites include the brain, bones, adrenal glands (endocrine glands that release hormones), and liver.
Only cancers that begin in the tissues of the lungs, typically in the cells lining the air passages, are called “lung cancer.” Cancer from other parts of the body may spread (or metastasize) to the lungs, but these cancers are not called lung cancer. For example, breast cancer that spreads to the lungs is still breast cancer and will be treated as breast cancer, not lung cancer. Lung cancer that spreads to the liver is treated as lung cancer, not liver cancer.