Among the additional tests that are available, screening breast MRI and screening breast ultrasound have been tested extensively. Background breast density has less impact on the ability of MRI and ultrasound to detect cancer than it does for mammography, which is why either of these tests increases cancer detection over mammography alone, MRI much more so than ultrasound. However, both MRI and ultrasound are associated with a much higher rate of benign biopsies and a much higher rate of recommendation for short-interval follow-up than mammography. Therefore, choosing to have one of these tests in addition to mammography involves the benefit/risk trade-off of early cancer detection versus increased false positives. The higher the cancer risk, the more likely there will be benefit, so the trade-off is more favorable for high risk women than for average-risk women who simply have dense breasts.
Screening breast tomosynthesis (sometimes referred to in advertising as "3D mammography") is currently being introduced into some radiology practices, but its use has not been as completely studied as either MRI or ultrasound. Population-based screening trials indicate that tomosynthesis increases breast cancer detection similar to ultrasound (although not as much as MRI), and that tomosynthesis decreases the rate of false positives, even below that seen in screening mammography. However, we await more robust evidence on the benefits and limitations of tomosynthesis. At this point, availability of tomosynthesis may be limited.