As primary care providers define the individual breast cancer risk for their patients with dense breasts, they will need to consider the possible need for supplemental screening. The three primary modalities for supplemental imaging are magnetic resonance imaging (MRI), whole breast ultrasound, and digital breast tomosynthesis (DBT), which are described below. Before ordering these diagnostic tests, providers must recognize three key points:
- These supplemental screening tests can all increase cancer detection
- None of these supplemental tests are proven to decrease mortality or morbidity from breast cancer
- Currently, no major organization has recommended the use of supplemental screening based on breast density characteristics, alone
Magnetic Resonance Imaging (MRI)
Contrast enhanced MRI has been recommended as an adjunct to mammography screening in women at high risk for breast cancer (such as BRCA or other gene mutation carriers, other high-risk genetic syndromes, those with a history of thoracic radiation before the age of 30 or a >20% lifetime risk of breast cancer). MRI depicts a functional image of the breasts. The sensitivity of breast MRI for cancer detection is greater than mammography alone, or mammography performed in conjunction with breast ultrasound resulting in up to 14.7 additional cancers detected per 1000 women screened in a high risk population.1 The downside of MRI is a higher recall rate for additional imaging than mammography, alone, and a lower positive predictive value.
Screening breast MRI for cancer detection requires intravenous injection of gadolinium contrast and prone positioning of the patient. MRI is not recommended for pregnant women, those with pacemakers or other incompatible implanted material, patients with impaired renal function, or those with severe claustrophobia. There is no ionizing radiation.
The use of screening whole breast ultrasound as an adjunct to mammography is indicated in high-risk patients who cannot tolerate MRI. In women with dense breasts, supplemental screening with whole breast ultrasound increases the cancer detection rate over that of screening mammography, alone. Recent reports have described the experience of supplemental screening with breast ultrasound in the state of Connecticut where breast density legislation was previously enacted. In studies of women with dense breasts and varying levels of breast cancer risk, 1.8 to 3.2 additional cancers per 1000 women were reported. However, this was with a high false positive rate and very low positive predictive value as low as 5.5%. 2-4
Ultrasound is performed using a high-frequency ultrasound transducer and application of a water-soluble gel to the breast. There is no ionizing radiation.
Digital Breast Tomosynthesis (DBT) is a 3-dimensional (3-D) x-ray mammogram imaging technology that, in early performance studies, has been shown to increase cancer detection over conventional mammography, alone, estimated at 1- 2 additional cancers per 1000 women.5 An added benefit is that DBT has also been shown to decrease recall rates by making it easier to confirm normal overlapping tissue as opposed to a suspicious mass. This results in fewer false positive mammogram studies.
Multiple images of a compressed breast are reconstructed into high resolution slices which ultimately permit increased cancer detection in women with and without dense breasts. As with all mammography studies, performance may be limited, somewhat, in patients with the densest breasts. At the beginning of its use, DBT was associated with a higher radiation dose than traditional 2-D mammography; however, the current use of synthesized 2-D images from the 3-D acquisitions results in radiation exposure similar to conventional 2-D mammography depending on which images are acquired. DBT has been approved by the Food and Drug Administration (FDA) for breast cancer screening. Access to the screening tool may be limited as the technology is still relatively new.
Molecular Breast Imaging
Molecular Breast Imaging (MBI) is a radioisotope study which depicts a functional image of the breast. In early studies MBI has been shown to increase cancer detection over conventional mammography, alone, with a high sensitivity and specificity as well as 7 – 8 additional cancers detected per 1000 studies.6 Unfortunately recall rates are higher than conventional mammography.
MBI requires the intravenous injection of 99mTc-Sestamibi. There have been concerns regarding radiation dosage associated with radioisotope breast imaging techniques. Given recent technological advances, radiation exposure for MBI now approaches that of conventional mammography; however, the exposure occurs to the whole body, not just the breasts. This is not widely used in screening. Availability is limited as this is a relatively new technology for this purpose.
- Berg et al, JAMA 2012; 307:1394-1404
- Hooley et al, Radiology, 2012; 265(1):59-69.
- Weigert et al, Breast Journal 2012; 18(6): 517–522.
- Parris et al, Breast Journal 2013; 19(1): 64–70.
- Friedewald, et al, JAMA 2014;311(24):2499-2507
- Rhodes et al. AJR 2015; 204:241–251