Progress and Disparities in Lung Cancer Screening in Japan: A Bayesian Analysis Toward Achieving Health Japan 21 Targets

Background: Japan’s national health promotion plan, Health Japan 21, aims to achieve 60% lung cancer screening coverage by 2028. This study projected screening uptake through 2028 and estimated the probability of achieving this target at the national and prefectural levels, stratified by gender. Methods: We analyzed lung cancer screening in Japan using the Comprehensive Survey of Living Conditions data (2013, 2016, 2019, 2022) for adults aged 40–69. Bayesian linear regressions estimated trends in logit-transformed screening coverage, with projections through 2028. We estimated annual changes, the probability of reaching 60% by 2028, and the first year in which the probability of target attainment exceeded 80%. Results: National screening coverage increased from 42.3% in 2013 to 49.7% in 2022, with an annual percentage-point change of 0.83 (95% CrI: −0.20 to 1.80). At this rate, the probability of reaching 60% by 2028 is 12.2%. Only 11 of 47 prefectures are projected to meet the target, while 4 (Kyoto, Kumamoto, Kagoshima, and Okinawa) are unlikely to reach it. Sex disparities were observed, with the probability of achievement at 25.4% for men versus 7.1% for women. The female annual change (0.99) exceeded the male annual change (0.65). Conclusions: Lung cancer screening participation varies significantly across regions and between genders, reflecting uneven progress toward the national goal. If current trends continue, achieving 60% coverage by 2028 will be challenging for most prefectures. Policy and system reforms could speed up uptake by focusing on prefectures and populations with the lowest participation rates.