Lung cancer is the uncontrolled growth of abnormal cells in the lung. Majority of people who get lung cancer have been cigarette smokers, but not all people who smoke get lung cancer. And, some people who have never smoked get lung cancer. Normal lung tissue is made up of cells that are programmed by nature to create lungs of a certain shape and function.

Sometimes the instructions to a cell go haywire and that cell and its offspring reproduce wildly, without regard for the shape and function of a lung. That wild reproduction can form tumors that clog up the lung and make it stop functioning as it should. Because of the large size of the lungs, cancer may grow for many years, undetected, without causing suspicion. Lung cancer can spread outside the lungs without causing any symptoms. Adding to the confusion, the most common symptom of lung cancer, a persistent cough, can often be mistaken for a cold or bronchitis.