Results of a trial conducted by Rush University Medical Center showed that screening with low-dose spiral computed tomography (CT scan) not only reduces lung cancer deaths but would cost insurers less than colorectal, breast and cervical cancer screenings. The core of the cost-benefit calculation was a stage-shift model, in which an intervention -- in this case, lung cancer screening -- shifted the distribution of stages of cancer. The consequence of the stage shift was that more lung cancers were detected at an earlier stage. This leads to treatment costs that are earlier and lower, and to more people cured of or living with cancer. The current study model was designed to estimate the cost and cost-benefit of lung cancer screening for high-risk US smokers and former smokers ages 50 to 64, each of whom had smoked one or more packs of cigarettes a day for at least 30 years.