Introduction We developed a web-based decision aid (DA) to support shared decision making (SDM) during the clinical encounter between physicians and women with average breast cancer risk when deciding whether to participate in breast cancer screening (available on http://decidirmamografia.com.ar/). We aimed to assess its effect on informed decisions, SDM, knowledge of the benefits and risks of screening, decisional conflict and intentions to undergo screening mammography.

Methods We conducted a pragmatic ‘before-after’ trial, with 27 women aged 40 to 69 years old, with average breast cancer risk. Participants had an appointment with their primary care physicians using the DA and completed a pre and post-survey.

Results The median age was 56. After the use of the DA, 12 out of 27 patients (44%) made an informed choice compared to only one patient (3%) before the use of the DA, an absolute difference (AD) of 41% (95% CI: 19 to 63, p=0.0010); 55% had adequate knowledge compared to 7% before (AD: 48%; 95% CI: 26 to 71; p=0.0002); fewer women expressed positive attitudes towards screening (37 vs 88% before DA, AD: 51%; 95% CI: 74 to 29; p=0.0001); and fewer women intended to do a mammogram (48 vs 74% before DA, AD: 26%; 95% CI: 0 to 52 p=0.0654). Only one patient reported a high decisional conflict, and 80% of the patients considered that they made a shared decision with their physician.

Discussion This is the first DA for breast cancer screening developed and tested in Argentina. These results agree with similar trials that evaluated informed decisions.

Conclusions The implementation of this DA demonstrated that women made more informed choices based on adequate knowledge of the benefits and harms of breast cancer screening and their own values and preferences.