One of the most common and lethal forms of cancer in the US, lung cancer usually grows silently for years before symptoms arise that lead to diagnosis and treatment. By then, the cancer has typically reached an advanced stage where treatment is difficult and cure rates are low.  The National Lung Screening Trial (NLST) is the first scientific study that provides clear evidence that (computerized tomography (CT) screening significantly reduces the death rate due to lung cancer. NLST data shows 20 percent fewer lung cancer deaths among trial participants who had the CT scan compared with the chest x-ray. Until now, no screening test for lung cancer has proven effective in detecting tumors at an early, more treatable stage. The trial was conducted at 33 sites throughout the country and included more than 53,000 current or former “heavy smokers” between the ages of 55 and 74. Each participant was either a former heavy smoker within the last 15 years or a current smoker with at least a 30 pack year history of smoking (calculated by the number of packs per day times the number of years smoking). Between 2002 and 2004, the participants were randomly assigned to receive either a chest x-ray or a CT scan annually for three years. Then, they were monitored for the following five years. NLST data shows 20% fewer lung cancer deaths among trial participants who had the CT scan, as compared with the chest x-ray.