There are no national guidelines for using supplemental ultrasound screening (US) after a mammogram, explains Brian L. Sprague, MD. “Yet, the use of breast US has been increasing over the past decade in the United States, in part due to the growing focus on the limitations of mammography screening among women with dense breasts,” he says. “Although supplemental US may detect breast cancers missed by mammography, it requires additional imaging and may lead to unnecessary breast biopsies among women who do not have breast cancer. Therefore, it is important to use supplemental ultrasound only in women at high risk for having a breast cancer that is undetected by mammography screening.”

For a study published in Cancer, Dr. Sprague and colleagues sought to evaluate the breast cancer risk characteristics of women undergoing US in clinical practice.

Ultrasound Use Not Well Targeted for High-Risk Cases

The study team computed the risk for mammography screening failures—interval breast cancer and advanced cancer—among women undergoing US and compared it with women undergoing mammography alone. They used data from 32 healthcare facilities within three regional registries of the Breast Cancer Surveillance Consortium (BCSC). “We had access to data from more than 370,000 women who underwent a total of 38,166 screening ultrasound exams and 825,360 screening mammograms,” Dr. Sprague says. “For each imaging exam, we estimated the woman’s risk for invasive breast cancer, risk for interval cancer after a normal mammogram, and risk for advanced cancer using previously developed BCSC prediction models that depend on specific risk factors like family history of breast cancer, breast density, age, history of benign breast disease, and BMI.”

Dr. Sprague and colleagues observed that US in clinical practice is highly targeted to women with dense breasts, but not well targeted to those women who are at highest risk for an interval cancer or late-stage breast cancer diagnosis with mammography alone.

Dense Breasts, But at Low Risk for Mammogram Screening Failure

“A total of 95.3% of supplemental ultrasounds were performed in women with dense breasts, compared with 41.8% of mammograms without additional screening,” Dr. Sprague says. “Among women with dense breasts, a high risk for interval invasive breast cancer was present in 23.7% of women who underwent ultrasounds compared with 18.5% of women who had mammograms without additional imaging. The proportion with intermediate or high risk for advanced cancer was exceptionally close between the two groups (32.0% vs 30.5%). Thus, many women with dense breasts, but at low risk for a mammography screening failure (interval cancer or advanced cancer), underwent US, while numerous women at high risk of a mammography screening failure underwent mammography alone with no supplemental screening.”

The study also revealed women undergoing US had a similar distribution of invasive breast cancer risk compared with women undergoing mammography screening alone (Figure). When you restrict US to women with dense breasts, Dr. Sprague points out, the differences become even more modest. “Many women with low risk for invasive breast cancer underwent US, while many women at high risk of breast cancer underwent mammography alone with no supplemental screening,” he says.

Supplemental US Weighs Additional Risk Factors

The study team recommends that women and their healthcare providers consider other risk factors in addition to breast density when deciding whether to undergo supplemental US. “The likelihood of an interval cancer or advanced stage breast cancer diagnosis among women undergoing mammography screening varies according to breast density and other risk factors,” Dr. Sprague says. “Risk calculators are available to the public, including one from the BCSC that estimates a woman’s 6-year risk for advanced breast cancer among patients undergoing annual or biennial mammography based on an array of breast cancer risk factors. Women with elevated breast cancer risk and dense breasts, and all women with high advanced cancer risk despite routine mammography, should consider supplemental US.”

Dr. Sprague adds that further study is needed to characterize US performance and long‐term outcomes according to risk for mammography screening failure. “We are currently evaluating the performance of supplemental US among women with dense breasts in community practice to better characterize the sensitivity and specificity of this screening modality according to patient characteristics,” he says. “We are also working on the development of improved risk prediction models for mammography screening outcomes by incorporating breast imaging features including artificial intelligence algorithms.”