The natural history of lung cancer estimated from the results of a randomized trial of screening

to estimate parameters of the natural history, using a model to simulate the disease process and the effects of screening. The results suggest that the period before clinical presentation during which lesions can be detected by screening is very short (seven to eight months). This implies that to detect three-quarters of all lung cancers by screening, two examinations per year are necessary, and that such a program would advance diagnosis by six months if there were complete participation. The results of the trial itself suggest that the benefit, in terms of a reduction in mortality from lung cancer, is likely to be very small.