Lung cancer, the third most common cancer in the United States, occurs when cells in the lungs grow abnormally and tumors develop. Smoking is the number one contributing factor of lung cancer, and people over the age of 50 who smoke are encouraged to get a lung cancer screening. Screening is important with lung cancer because people sometimes do not show symptoms until the cancer has progressed to an advanced stage – the sooner lung cancer is detected, the more options a patient has for treatment.