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I have a patient with dense breasts who desires supplemental screening. She is not at very high breast cancer risk and/or has no major risk factors. What should I recommend?


Screening MRI has not been studied in average-risk women with no known cancer diagnosis. However, if a patient expresses a desire to be screened with MRI, then a full risk assessment would be helpful. Even if a patient does not have strong risk factors for breast cancer, there are a number of minor risk factors, including breast density, which together may raise her to a sufficiently high risk. The American Cancer Society states that for intermediate risk women, with a 15-20% lifetime risk (this may include women with a history of atypia on biopsy or with a personal history of breast cancer), the decision to have a screening MRI should be made on a case-by-case basis using a shared decision-making approach.

The data on screening ultrasound is limited at this point. Mammography typically finds 6 to 8 breast cancers in every 1000 women screened for the first time. In women with dense breasts at average risk, small studies have shown ultrasound can detect 1.6 to 4 mammographically occult cancers for every 1000 women screened for the first time. Therefore, supplemental ultrasound adds substantially to the cancer yield in some studies. The majority of cancers found on ultrasound are smaller than 1 cm and are invasive.

However, there are two major drawbacks to the currently available data. The first is that no studies have been performed with control groups and long-term follow-up. Thus, we do not know what the clinical impact of finding these additional small cancers is - specifically whether the cancers would otherwise be detected at the next mammography screen while still small, node-negative, and at early stage, and whether there is any impact on mortality. The second drawback is that many more biopsies are generated by screening ultrasound than screening mammography, and most of these additional biopsy recommendations ultimately end up being false positives. The positive biopsy rate for lesions detected on screening mammography is 25% to 40%, while the positive biopsy rate for lesions found on screening ultrasound is 5-10%. This means that 90% to 95% of biopsies initiated by the screening ultrasound in women with negative mammograms end up showing no cancer.

Due to these concerns, there is no formal recommendation from the radiology community at this point regarding screening ultrasound. Some radiologists are opposed to it, while some believe that it has a role. The results of screening breast ultrasound may be more favorable in centers with a dedicated program.
Whichever supplemental screening test is being considered, it is important to keep in mind that for patients who are not high risk, the a priori probability of breast cancer is low. Therefore, the benefit of additional screening is diminished, whereas the potential harms remain the same.