Supporting women to make well-informed decisions about breast cancer screening requires effective communication about possible outcomes including overdetection or overdiagnosis (diagnosis and treatment of cancers that would never become clinically evident). We investigated the effects, over 2 years of follow-up, of providing information about overdetection to women considering breast screening.
Participants were women aged 48–50, without personal or strong family history of breast cancer, who had not undergone mammography in the past 2 years. We randomised 879 women to receive the intervention decision aid (evidence-based information on overdetection, breast cancer mortality reduction, and false positives) or a control decision aid (identical but without overdetection information). Telephone interviews at post-intervention (n=838), 6 months (n=790), 1 year (n=756), and 2 years (n=712) assessed screening knowledge, attitudes, intentions, and uptake.
Logistic regression analyses revealed significant group-by-time interactions for knowledge (p<0.01), attitudes (p<0.01), intentions (p<0.01), and screening uptake (p=0.05). Compared with controls, more women in the intervention group demonstrated adequate conceptual knowledge both post-intervention (OR 5.53, 95%CI 4.08–7.52) and 2 years later (OR 2.04, 95%CI 1.46–2.85). Post-intervention, fewer women in the intervention group had positive attitudes (OR 0.42, 95%CI 0.29–0.61) and intentions (OR 0.39, 95%CI 0.26–0.58); these differences dissipated by 2 years (attitudes OR 0.89, 95%CI 0.59–1.34; intentions OR 0.81, 95%CI 0.52–1.26). Slightly fewer women in the intervention group underwent mammography during the first 6 months of follow-up (OR 0.72, 95%CI 0.50–1.04), but after 2 years uptake was similar across groups (OR 0.96, 95%CI 0.73–1.26).
A brief decision aid led to long-lasting improvement in women’s understanding of potential consequences of breast screening, including overdetection. Although breast screening intentions were lower in the intervention group than among controls immediately post-intervention, after 2 years we have not observed an effect on mammography uptake.