If a patient has dense breasts, what additional screening tests are available after a mammogram?

Depending on the patient’s age, risk level (for further explanation see section on Risk Assessment Tools) and breast density, additional screening tools, such as ultrasound or MRI, may be recommended in addition to mammography. The addition of another imaging tool after a mammogram will find more cancers than mammography/tomosynthesis alone (see Table: Summary of Cancer Detection Rates by Screening Method).

It is important to reassure the patient that it is normal for any screening test to find things that may need to be looked at more closely by use of additional testing. While some of these additional findings may be cancerous, the vast majority will not (this is known as a “false positive”); the only way to determine the importance of such findings is through additional imaging and sometimes biopsy.

Both 2D and 3D mammograms are x-ray technologies. X-rays have difficulty penetrating dense tissue and, as such, are more effective in fatty breasts than in extremely dense breasts. Early results suggest that ultrasound finds additional cancers hidden by dense tissue even after 3D mammography, though further study is warranted.

Ultrasound: Ultrasound is the only screening test suggested specifically for women with dense breasts as a supplement to mammography. In dense tissue, physician-performed or technologist-performed ultrasound has been shown to find an additional 2-4 cancers per 1000 women already screened by 2D or 3D/tomosynthesis mammography. Automated whole breast ultrasound, using special equipment, results in detection of another 2-3 cancers per 1000 women screened. Like all screening tools, ultrasound also detects many findings that are not cancer, but that may require follow-up imaging and/or biopsy. There is no x-ray radiation from ultrasound.

MRI: Contrast-Enhanced Magnetic Resonance Imaging (MRI) can find the most breast cancers of any imaging test currently in widespread use. Breast MRI reveals an average of 10 additional cancers per 1000 women screened after mammography, even when both mammography and ultrasound have been performed. The cancer-detection benefit is seen across all breast density categories.

A woman at very high risk for breast cancer (due to a known or suspected mutation in a breast cancer causing gene, or due to a greater than 20% lifetime risk for breast cancer according to the Claus, Tyrer-Cuzick, or other model that predicts risk for pathogenic BRCA mutation [1]) may be eligible to begin screening at age 25, or at least by age 30. In high-risk women, MRI is recommended annually, in addition to mammography, regardless of breast density, though before age 30 sometimes only MRI is performed due to the radiation sensitivity of younger breast tissue. Annual screening MRI is also recommended in women who have had prior radiation therapy to the chest at least 8 years earlier and before age 30, such as for Hodgkin’s lymphoma. Recently, the American College of Radiology recommended annual screening MRI also in women with a personal history of breast cancer diagnosed by age 50, and in women diagnosed later who have dense breasts [2]. Annual supplemental screening MRI can also be considered in women who have a personal history of atypical or risk lesions, such as lobular carcinoma in situ.

MRI of the breasts requires intravenous injection of gadolinium-based contrast and lying in a tunnel-like space that may be difficult for women with claustrophobia. There is no x-ray radiation from MRI. Gadolinium has been shown to accumulate in parts of the brain, but no adverse effects have been shown from this.

MRIs have many false positives (when additional testing or biopsy is recommended for a finding which is not cancer). The benefits and risks of MRI in women who are not at high risk are being studied. In most centers, MRI is a very expensive imaging test that is not covered by insurance unless a woman meets high-risk definitions, and a copay and/or deductible may be incurred. MRI cannot be performed in women with poor kidney function, pacemakers, or certain other metal implants.

The addition of screening ultrasound is usually only recommended in women with dense breasts. Screening MRI is used in high-risk women of all breast densities. If screening MRI is performed, there is no need for screening ultrasound.

Screening MBI and Contrast-Enhanced Mammography may be offered to women with dense breasts or as an alternative to MRI at some centers. Further validation of such approaches is in progress.