Evaluation of a mobile mammography unit: concepts and randomized cluster trial protocol of a population health intervention research to reduce breast cancer screening inequalities

Background Breast cancer is the leading cancer in women in France both in incidence and mortality. Organized breast cancer screening (OBCS) has been implemented nationwide since 2004, but the participation rate remains low (48%) and inequalities in participation have been reported. Facilities such as mobile mammography units could be effective to increase participation in OBCS and reduce inequalities, especially areas underserved in screening. Our main objective is to evaluate the impact of a mobile unit and to establish how it could be used to tackle territorial inequalities in OBCS participation. Methods A collaborative project will be conducted as a randomized controlled cluster trial in 2022-2024 in remote areas of four French departments. Small geographic areas were constructed by clustering women eligible to OBCS, according to distance to the nearest radiology centre, until an expected sample of eligible women was attained, as determined by logistic and financial constraints. Intervention areas were then selected by randomization in parallel groups. The main intervention is to propose an appointment at the mobile unit in addition to current OBCS in these remote areas according to the principle of proportionate universalism. A few weeks before the intervention, OBCS will be promoted with a specific information campaign and corresponding tools, applying the principle of multilevel, intersectoral and community empowerment to tackle inequalities. Discussion This randomized controlled trial will provide a high level of evidence in assessing the effects of mobile unit on participation and inequalities. Contextual factors impacting the intervention will be a key focus in this evaluation. Quantitative analyses will be complemented by qualitative analyses to investigate the causal mechanisms affecting the effectiveness of the intervention and to establish how the findings can be applied at national level. Trial registration Registered on ClinicalTrials.gov, December 21, 2021: NCT05164874. Keywords: Breast cancer screening, Mobile mammography, Social and territorial inequalities, Randomized cluster trial, Population health intervention research