Lung cancer is the uncontrolled growth of abnormal cells in one or both of the lungs.
While normal lung tissue consists of cells programmed by nature to reproduce and develop into healthy, well-formed lungs, these abnormal cells reproduce rapidly and disrupt this natural programming. Lung cancer almost always begins in one lung, and then spreads to lymph nodes or other tissues in the chest, including the other lung. Lung cancer can also metastasize throughout the body, spreading to the bones, brain, liver, or other organs. Since the lungs are large, cancers can grow in them for many years before they are detected. In fact, lung cancers can easily spread outside the lungs without causing any symptoms.