Several prior pilot trials suggest MRI may be beneficial in detecting clinically and mammographically occult breast cancers in women at high risk for breast cancer. However, the use of biopsy and cancer yield varies widely across single site pilot studies. The purpose of our study was to compare performance of screening mammography vs. MRI in women at genetically high risk for breast cancer.

We conducted a multi-institution international prospective study of screening mammography and MRI in women > 25 years of age who were genetically high risk, defined as BRCA1 or BRCA2 carriers or with at least a 25% lifetime risk for breast cancer determined by either the Claus, Gail, Couch, or Berry-Parmigiani risk models. Women with a history of breast cancer were eligible for a contralateral screen if diagnosed within 5 years or a bilateral screen if diagnosis was greater than 5 years. All exams (MRI, mammography, and clinical breast exam) were performed within 90 days of each other.

A total of 390 eligible women were enrolled at 13 sites over a 30 month period and 367 women completed all study exams. Imaging evaluations recommended 38 biopsies and 27 were performed resulting in four cancers for an overall 1.1% cancer yield (95% CI is 0.3% to 2.8%). MRI detected all 4 cancers while mammography detected only 1. The diagnostic yields of MR vs. mammography were 1.1% and 0.3% respectively; thus, the added cancer yield of MRI was 0.8% (95% CI is 0.2% to 2.4%). The biopsy recommendation rates for MRI and mammography were 8.5% (95% CI is 5.8% to 11.8%) and 2.2% (95% CI is 0.1% to 4.3%). The positive predictive values of MRI and mammography were similar at 12.9% (95% CI is 3.6% to 30%) and 12.5%(95% CI is 0.3% to 52.7%).

Screening MRI in high risk women can detect mammographically and clinically occult breast cancer. Screening MRI resulted in 6% of women with a negative mammogram and CBE being recommended for biopsy.