Comparative effectiveness of breast MRI and mammography in screening young women with elevated risk of developing breast cancer: a retrospective cohort study.

Screening guidelines recommend that women with 20 % or greater lifetime risk of breast cancer undergo annual breast MRI screening to supplement mammography, irrespective of age. In patients less than 40 years, mammography is often avoided due to concerns about radiation and decreased performance. However, prior studies have been limited by large percentages of women above 40 with decreased breast density. Our purpose was to test whether adding mammography to breast MRI screening compared to breast MRI screening alone in women below 40 increases cancer detection rates. After obtaining IRB approval, chart review identified patients aged 25-40 years undergoing breast MR screening (2005-2014). Demographics, risk factors, BI-RADS assessments, background parenchymal enhancement, and mammographic breast tissue density were recorded. Cancer detection rates, short-term follow-up (BIRADS 3), image-guided biopsy (BIRADS 4,5), and PPV1-3 were calculated. 342 breast MRI exams were identified (average age was 33, 37 % were nulliparous, and 64 % had prior benign biopsy), 226 (66 %) of which underwent concurrent mammography. Risk factors included 64 % with breast cancer in first-degree relative(s), 90 % had heterogeneous or extremely dense breast tissue on mammography, and 16 % were BRCA carriers. Four invasive cancers were detected by MRI (11.7 cancers/1000 examinations, 95 % CI 8.3, 15.1). None of these was detected by mammography, and no cancers were independently identified by mammography. Breast MRI screening in high-risk women under 40 yielded elevated cancer detection rates (11.7/1000). The cancer detection rate for mammography was 0 %, suggesting that MRI alone may be useful in screening high-risk women under 40.