A case-control study for evaluating lung cancer screening in Japan.

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Lung cancer screening using chest X-ray examination and sputum cytology was introduced by the Japanese government in 1987. However, there was no direct evidence of the benefit from lung cancer screening in terms of reduction of mortality at that time. A case-control study was conducted using the data from 50 areas in which population-based lung cancer screening programs had been conducted for several years. Case series consisted of 273 deceased lung cancer cases, and 1269 control patients were collected from those who were alive at the time of diagnosis of the corresponding case: These were matched by gender, age, smoking status, and type of health insurance. Screening histories, which were obtained from the list of screenees, were compared between cases and matched controls for the identical calendar period before the time of diagnosis of the case. The odds ratio for dying from lung cancer for those who were screened within 12 months compared with those who were not screened was 0.72 (95% confidence interval, 0.50-1.03). When divided by gender, the odds ratio was significantly decreased in females. The authors interpreted these data to indicate that there is a small positive effect of lung cancer screening in terms of reducing mortality due to lung cancer. However, this small effect cannot be evaluated adequately by observational studies, such as case- control studies, because of the self-selection bias. Discussion is needed to determine the resources that should be allocated to this issue for developing an effective strategy for lung cancer control.