Improving participation in breast cancer screening through a tailored reminder letter: a randomized controlled trial tackling socioeconomic inequities

Organized breast cancer (BC) screening facilitates early detection, improving treatment outcomes and reducing mortality. In Flanders, Belgium, participation in the Breast Cancer Screening Program is associated with substantial reductions in BC-specific mortality. However, participation remains suboptimal and socially patterned, with rates falling below 40% in areas with average income around the poverty line. In this trial, we evaluated whether a culturally and linguistically tailored reminder letter increases mammographic screening among non-responders and reduces socioeconomic disparities in participation. A tailored reminder letter was co-created with women of low socioeconomic status (SES) and sector experts. Its effectiveness among screening non-responders was evaluated in a two-arm, parallel-group, superiority randomized controlled trial (RCT) conducted between April and June 2024. In total, 7,922 non-attenders were randomized 1:1 to receive either the standard invitation alone (control) or the standard invitation plus the tailored reminder (intervention). Screening participation within 40 days was compared between groups using crude odds ratios (ORs) with 95% confidence intervals (CIs), and statistical significance was assessed using χ² tests; analyses were further stratified by SES. This trial was registered at ClinicalTrials.gov (NCT07472036; registered retrospectively on 13/03/2026). Overall, 997 (12.6%) participants attended screening within 40 days. Participation was higher in the intervention arm (15.8%) than in the control arm (9.4%), corresponding to a 6.4% absolute increase (OR 1.81, 95% CI 1.58–2.07). Overall, 27.0% of participants were classified as low-SES. The intervention effect was larger among low-SES individuals (+ 8%, from 4.0% to 12.0%; OR 3.24, 95% CI 2.27–4.61) than among non–low-SES individuals (+ 5.2%, from 11.7% to 16.9%; OR 1.53, 95% CI 1.31–1.79). A tailored reminder strategy increased BC screening participation while reducing socioeconomic disparities, highlighting the potential of equity-oriented communication strategies to strengthen population-based screening programs relying on centralized invitation systems.