Pro: Motoyasu Sagawa1; Makoto Sugita1; Tsutomu Sakuma ABSTRACT-Although the results of randomized controlled trials (RCTs) are usually more reliable than that of case-control studies, not all RCTs reflect the truth. RCT concerning mass screening is very difficult to conduct properly because of the large number of participants and the long study period. For example, compliance and contamination in the Mayo Lung Project were reported 75% and 73%, respectively. The results of RCTs evaluating the

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... ficacy of lung cancer screening, mainly in the 1970s, failed to show that lung cancer mortality would decrease by screening. There were four case-control studies evaluating the efficacy of lung cancer screening in the 1980s-early 1990s. In two of them, the results did not show screening efficacy, whereas another study showed that screening significantly reduced the risk for lung cancer deaths. The remaining study suggested that screening could reduce the risk for lung cancer deaths, but not significantly. Recently four other case-control studies evaluating the efficacy of lung cancer screening in 1990s were reported from Japan. The results of three studies showed significant reduction of the risk for lung cancer deaths by screening, and the results of the remaining study indicated a similar trend. The latest four case-control studies are reliable to evaluate the efficacy of current lung cancer screening systems. Problems and future studies in lung cancer screening systems are also discussed. (JJLC. 2002; 42: 741-745)