Effect of an information leaflet on breast cancer screening participation: A cluster randomized controlled trial.

To evaluate the impact of an information leaflet about the risk-benefit balance of breast cancer screening on women's participation. This cluster randomized controlled trial was conducted within a population-based breast cancer screening program and included women from the catchment areas of two hospitals in Barcelona, Spain. We evaluated women aged 50-69 years invited to screening between September 2019 and January 2020. The intervention group received an information leaflet on the benefits and harms of mammography screening. The control group received the usual invitation letter. The clusters consisted of the processing days of the invitation letter, assigned to the intervention with a simple random allocation scheme. We compared the participation rate at the individual level between groups, stratified by hospital and by per-protocol and intention-to-treat analyses. We included 11,119 women (137 clusters): 5416 in the intervention group (66 clusters) and 5703 in the control group (71 clusters). A total of 36% (1964/5393) of the women in the intervention group and 37% (2135/5694) of those in the control group attended screening, respectively. Overall, we found no differences in participation among groups (difference in participation - 1.1%; 95%CI; - 2.9 to 0.7%). In a hospital attending a population with a low socioeconomic status, attendance was lower in the intervention group (- 1.4, 95%CI: - 5.7% to - 0.03%). Overall participation in our program was unaffected by a new information leaflet on the risk-benefit balance of breast cancer screening. However, participation was lower in certain populations with lower socioeconomic status TRIAL REGISTRATION: Trial registration number ISRCTN13848929 .