In Reply Dr Liao is correct in regard to comments on our recent cohort study1: because low-dose computed tomography screening is not covered by national health insurance in Taiwan (and no claims exist), we do not know precisely who was screened. What we do know, however, is that screening was widely promoted to Taiwanese women, and the resulting effect on their stage-specific lung cancer incidence was a dramatic rise in early-stage disease accompanied by stable late-stage disease. This signature is consistent with overdiagnosis, either as a result of screening or widespread incidental detection. If there were an increase in true cancer occurrence (perhaps owing to worsening occupational exposure or air pollution, as Dr Liao suggested), early-stage and late-stage disease would be expected to rise in tandem.2
