An Alternative Approach to Selecting Patients for High-risk Screening with Breast MRI

Abstract

Current guidelines for adding breast MRI to annual screening mammography are based entirely upon stratification of risk, with a heavy focus on lifetime calculations. This approach is fraught with difficulty due to the reliance on mathematical models that vary widely in their calculations, the inherent age discrimination of using lifetime risks rather than short-term incidence, and the failure to incorporate mammographic density, the latter being an independent risk as well as the greatest predictor of mammographic failure. By utilizing a system of patient selection similar to what was used in the American College of Radiology Imaging Network (ACRIN) 6666 trial for multi-modality imaging, 33 women without a prior diagnosis of breast cancer were found to harbor mammographically occult carcinoma through MRI screening. These 33 patients represent a 2% yield, closely approximating the yields seen in prospective MRI screening trials of women at very high risk of breast cancer. Using the "~20-25%" minimum established by the American Cancer Society and later the National Comprehensive Cancer Network, the Gail model would have prompted the use of MRI in only 9 of 33 (27.3%) patients, the Claus model 1 of 33 (3%), and the Tyrer-Cuzick model 12 of 33 (36.4%). Using all three models and opting for the highest calculated risk, then including BRCA-positivity, still would have identified only 16 of 33 (48.5%) patients with occult breast cancer discovered by MRI. Only one patient was BRCA-positive, and none had lobular carcinoma in situ, while 6 of 33 patients (18.2%) had atypical ductal hyperplasia (ADH). Measures are proposed to refine patient selection for MRI screening through the use of short-term or categorical risks, mammographic density, while maintaining cost-effectiveness through longer MRI screening intervals.