Risk of leukemia among participants of gastric mass screening survey in Japan: a population-based, case-control study

To assess the risks of leukemia for individuals participating in a gastric mass screening program using barium photofluorographic examination in Japan, a population-based, case-control study was carried out. The histories of participation in the last 10 years of 79 leukemia cases diagnosed between 1978 and 1985 and twofold controls matched for sex, age (+/- 5 years), and residence were investigated using the records of the gastric mass screening program. The odds ratio of any type of leukemia for those participating at least once in the last 10 years was 1.09 (95% confidence interval, 0.61-1.96) and that of myeloid type was 0.88 (95% confidence interval, 0.38-2.27). Even when the histories of the preceding 5 years were ignored, no significant excess risks were found among patients with any type and myeloid type of leukemia. These results suggest that there is insufficient evidence to support the positive association between the incidence of leukemia and participation in gastric mass screening. The limitations and implications of this analysis are discussed.