MRI versus mammography plus ultrasound in women at intermediate breast cancer risk: study design and protocol of the MRIB multicentre randomized controlled trial

Background In women at high/intermediate lifetime risk of breast cancer (BC-LTR), contrast-enhanced magnetic resonance imaging (MRI) added to mammography ±ultrasound (Mx±US) increases sensitivity but decreases specificity. An alternative strategy, MRI alone, potentially more cost-effective, has never been explored. This study aims to assess the characteristics of women who participated in a randomized trial offering MRI alone. Methods In this feasibility multicentre randomized controlled trial we compared MRI alone versus Mx+US in women at intermediate BC-risk (allocation ratio 1:1). Eligible women were aged 40 –59, with a 15–30% LTR and/or extremely dense breasts. Two screening rounds per woman were planned in ten centres experienced in MRI screening. Primary endpoint: rate of cancers detected in the two arms after 5 years of follow-up. Secondary endpoints: distribution of the risk profiles among the women enrolled in the trial; distribution of pathological stages and histology of cancers detected; interval cancer rate in the two arms. Results From 07/2013 to 11/2015, 1,254 women (mean age 47 years) were enrolled: 624 were assigned to Mx+US, 630 to MRI. Most of them were aged below 50 (72%) and premenopausal (45%), 52% used oral contraceptives. Among postmenopausal women, 15% had used hormone replacement therapy. Breast and/or ovarian cancer in mother and/or sisters were reported by 37% of enrolled women, extreme breast density was recorded for 79%, 41% had a 15–30% BC-LTR. Conclusions The distribution of BC-risk profile major determinants (breast density and family of breast and ovarian cancer) of enrolled women varied across centres. Trial registration NCT02210546 Key points Mammography plus ultrasound are commonly used to screen women with dense breasts Supplemental ultrasound increases BC detection rate but also false-positives and potential overdiagnosis Whether increased BC detection by US translates into reduced mortality is unknown MRI alone could be more risk- and cost-effective than mammography plus ultrasound