The shape of the time-signal intensity curve is an important criterion in differentiating benign and malignant enhancing lesions in dynamic breast MR imaging. A type III time course is a strong indicator of malignancy and is independent of other criteria.

Mammography alone, and also mammography combined with breast ultrasound, seems insufficient for early diagnosis of breast cancer in women who are at increased familial risk with or without documented BRCA mutation. If MRI is used for surveillance, diagnosis of intraductal and invasive familial or hereditary cancer is achieved with a significantly higher sensitivity and at a more favorable stage.

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The accuracy of MR imaging is significantly higher than that of conventional imaging in screening high-risk women. Difficulties can be caused by an atypical manifestation of hereditary breast cancers at both conventional and MR imaging and by contrast material enhancement associated with hormonal stimulation.

In women at elevated familial risk, quality-assured MRI screening shifts the distribution of screen-detected breast cancers toward the preinvasive stage. In women undergoing quality-assured MRI annually, neither mammography, nor annual or half-yearly ultrasound or CBE will add to the cancer yield achieved by MRI alone.

Purpose To investigate the utility and accuracy of breast magnetic resonance (MR) imaging as a supplemental screening tool in women at average risk for breast cancer and to investigate the types of cancer detected with MR imaging screening. Materials and Methods This prospective observational study was conducted at two academic breast centers in women aged 40-70 years without breast cancer-associated risk factors (lifetime risk <15%). Between January 2005 and December 2013, women with at least minimal residual breast tissue (American College of Radiology categories A-D) and normal conventional imaging findings (screening mammography with or without screening ultrasonography [US]) were invited to undergo supplemental MR imaging screening. Outcome measures were supplemental cancer detection rates, interval cancer rates, and biologic profiles of MR imaging-detected additional cancers, as well as specificity and positive predictive value (PPV) of MR imaging screening. Tissue diagnoses or 2 years of follow-up were used to establish the reference standard. Results A total of 2120 women were recruited and underwent 3861 screening MR imaging studies, covering an observation period of 7007 women-years. Breast MR imaging depicted 60 additional breast cancers (ductal carcinoma in situ, n = 20; invasive carcinoma, n = 40) for an overall supplemental cancer detection rate of 15.5 per 1000 cases (95% confidence interval [CI]: 11.9, 20.0). Forty-eight additional cancers were detected with MR imaging at initial screening (supplemental cancer detection rate, 22.6 per 1000 cases). During the 1741 subsequent screening rounds, 12 of 13 incident cancers were found with MR imaging alone (supplemental cancer detection rate, 6.9 per 1000 cases). One cancer was diagnosed with all three methods (mammography, US, and MR imaging), and none were diagnosed with mammography only or US only. Cancers diagnosed with MR imaging were small (median, 8 mm), node negative in 93.4% of cases, and dedifferentiated (high-grade cancer) in 41.7% of cases at prevalence screening and 46.0% of cases at incidence screening. No interval cancers were observed. MR imaging screening offered high specificity (97.1%; 95% CI: 96.5, 97.6) and high PPV (35.7%; 95% CI: 28.9, 43.1). Conclusion In women at average risk for breast cancer, MR imaging screening improves early diagnosis of prognostically relevant breast cancer. RSNA, 2017 Online supplemental material is available for this article.

MR imaging-guided stereotactic hook-wire placement and excisional biopsy are accurate and effective in managing lesions identified at only breast MR imaging. MR imaging-guided core biopsy holds promise for allowing a definite work-up of these lesions.

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