Abstract
Lung cancer kills more people than any other cancer worldwide. Studies of screening for lung cancer using low-dose CT have been carried out at many institutions in different countries from 1993 through 2007. Over 100,000 asymptomatic persons, mainly those at risk for lung cancer were screened. All of the studies showed a high proportion of stage I diagnosis ranging from 77-100%. International Early Lung Cancer Action Program Investigators (I-ELCAP) screened 31,567 persons. The screening resulted in a diagnosis lung cancer in 484 participants. Of these participants, 412 (85%) had clinical stage I lung cancer, and the estimated 10-year survival rate was 88%. Case studies by the Anti-Lung Cancer Association (ALCA) and Hitachi investigators demonstrated the presence of a stage shift. The stage shift suggests a decrease in lung cancer mortality. ALCA and Hitachi investigators carried out the repeat screening over 14 years and 7 years respectively. Only after the fourth year of screening does the mortality rate start to decrease. Iinuma reported that the mortality reduction of the screened cancer is to be measured, the cumulative number of deaths should be observed and confirmed between the study group and control group and the ratio of the 2 groups are calculated in order to obtain the relative risk (RR) of death between the 2 groups. A mathematical simulation model was employed to calculate the values of RR after the prevalence screening using data from ALCA. The cumulative number of deaths should be counted from only those found in the repeated screening following the initial, prevalence screening. Iinuma predicts the reduction of lung cancer mortality in Japan in the year 2025 employing lung cancer screening CT (LSCT) and proposes a realistic method to achieve this goal. It is possible to reduce the lung cancer mortality in Japan by 22%, if we can perform LSCT screening in more than 50% of population aged 40-85 years old in 2025. We do not yet have sufficient data from well designed randomized controlled trials or cohort studies for CT lung cancer screening. However, the results of case studies have shown that repeat CT screening over 5 years can detect lung cancer which is curable. It is a very important task for us to study the effectiveness of CT screening for asbestos-related diseases. Cost-effectiveness analyses have shown that CT screening for lung cancer is very cost-effective.
