Like all the other organs of the body, the lungs are made up of many types of cells. Normally, cells divide to produce more cells only when the body needs them. This orderly process helps keep us healthy. If cells divide when new cells are not needed, a mass of tissue forms. This mass of excessive tissue, called a growth or tumor, can be benign, or malignant.
Benign tumors are self-contained.
They do not invade other areas, and may grow very slowly. Benign tumors often form a rounded mass that is easy to remove. Malignant tumors may grow at variable rates, some more rapidly than others. They tend to spread to surrounding normal areas and replace or take over normal tissues or organs. These cancer classifications derive their names from their microscopic appearance.