SummaryThe aim of this study was to evaluate the usefulness of annual screening for lung cancer by low-dose computed tomography (CT) and the characteristics of identified lung cancers. Subjects consisted of 5483 general population aged 40-74 years, who received initial CT scans in 1996, followed by repeat annual scans for most subjects in 1997 and 1998, with a total of 13 786 scans taken during 1996-1998. Work-up examinations for patients with suspicious lesions were conducted using diagnostic CTs. The initial screening in 1996 detected suspicious nodules in 279 (5.1%) of 5483 subjects, and 22 (8%) were confirmed surgically to have lung cancer. Corresponding figures in 1997 and 1998 screening studies were 173 (3.9%) of 4425 and 25 (14%) of 173, and 136 (3.5%) of 3878 and 9 (7%) of 136, respectively. The sensitivity and specificity of detecting surgically confirmed lung cancer were 55% (22/40) and 95% (4960/5199) in 1996 and 83% (25/30) and 97% (4113/4252) in 1997 screening, respectively. 88% (55/60) of lung cancers identified on screening and surgically confirmed were AJCC stage IA. Our trial allowed detection of nearly 11 times the expected annual number of early lung cancers. Repeat CT allowed the detection of more aggressive, rapidly growing lung cancers, compared to those in the initial screening. 25-32 © 2001 Cancer Research Campaign doi: 10.1054/ bjoc.2000.1531 available online at http://www.idealibrary.com on http://www.bjcancer.com to 150 detected SSPNs from these screenees. A much larger series of SSPN is required to study the second question, the prevalence of malignancy among the detected SSPNs, by getting an appreciable number of malignant SSPN, because the prevalence of malignant SSPN among high-risk population is estimated to be of the order of 1%. We defined our sample size of 5000 to 10 000, which was fairly larger than that indicated by Henschke et al, because we aimed to conduct our trial of CT screening for lung cancer using CT among the general population, which included never-smoked inhabitants in this rural area in Japan. In our study, inhabitants of 29 local municipalities in the Nagano Prefecture, Japan, who were 40 years of age or older were specifically requested in 1996 to volunteer for this programme. The annual mortality rate due to lung cancer in the same region was 37.3 per 100 000 population in 1998. Therefore, it was expected in our trial at least nearly 100 SSPNs be detected at each annual screening to undergo work-up examination, which would permit us to estimate the probability of CT-detected SSPN. Although we expected to encounter at least several cases with lung cancer among the total 5000 to 10 000 participants, we were not sure about the expected number of cancer cases because no information on this aspect was available. All subjects gave informed consent to receive base line and annual repeat CT scans of the thorax. SubjectsThe material of this study comprised a total of 13 786 CT examinations, including 5483 initial CT scans in 1996, 4425 first-year repeat CT scans in...

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