LAUSR

Abstract Objectives Despite evidence of breast cancer screening efficacy, the screening rate has remained less than 50% in Japan. This study aimed to evaluate the effect of an environmental approach offering on‐site mammography in workplaces. Methods Supermarket stores were randomly assigned into two groups, the intervention group (leaflet and mammography) and the control group (leaflet). From May to July 2018, participants in the intervention group were given a leaflet informing them of the subsidies for breast cancer screening and offered the opportunity to have mammography in their workplaces. Participants in the control group were given the same leaflet, but had to arrange their own screening outside the workplace. The primary outcome was the breast cancer screening rate in 2018. The odds ratio (OR) and 95% confidence interval (CI) for having screening in the intervention group compared with the control group were estimated using multilevel logistic regression. Results We analyzed data from 1624 participants (mean age 53 years) from 25 supermarket stores (intervention: 8 stores, control: 17 stores). Among participants who had not attended screening in the previous year, the screening rate was 7% in the control group and 53% in the intervention group, with an adjusted OR (95% CI) of 14.22 (8.97–22.54). The effect was greater in those who had never attended screening before. Conclusion In a worksite‐based cluster randomized controlled trial in Japanese supermarket stores, an environmental approach offering mammography in workplaces substantially increased the breast cancer screening rate within 1 year (UMIN000030465).