Study: Breast density alone should not guide supplemental screening decisions

Breast density notification laws have taken hold in 22 states and counting, yet questions remain about which patient should receive supplemental cancer screening. A newly published study this week has shed some light on the issue, showing that not all women with dense breast are at high risk for breast cancer.

However, by combining breast density with other risk factors, decisions about supplemental screening can better target the women with dense breasts who are at risk for an interval cancer between regular mammography appointments.

“By identifying women with a high likelihood of interval cancer who are also at higher risk for advanced disease, discussions of supplemental imaging or alternative screening methods can be directed to women who are more likely to benefit,” wrote Karla Kerlikowske, MD, of San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, and colleagues. Their findings were published this week in Annals of Internal Medicine.

The prospective cohort study included data from 365,426 women aged 40 to 74 who had undergone more than 800,000 screening mammography exams during the study period. Kerlikowske and colleagues noted each patient’s BI-RADS breast density assessment, as well as their five-year breast cancer risk as determined by the Breast Cancer Surveillance Consortium (BCSC) model, which includes factors such as age, history of breast biopsy, race/ethnicity and history of breast cancer in first-degree relatives. These factors were compared against cases of interval cancers in the study population. The authors defined a high interval cancer rate as more than one case per 1,000 examinations.

Results showed high interval cancer rates in two groups of patients. The first included women with a BCSC five-year risk of 1.67 percent and extremely dense breasts, and the second included women with a five-year risk of 2.5 percent and heterogeneously dense breast. Together, these groups made up 24 percent of all women with dense breasts.

Kerlikowske and colleagues also found that the interval rate of advanced-stage disease was highest in patients with a five-year risk of 2.5 percent or greater and either heterogeneously dense or extremely dense breasts. This group at risk for advanced-stage disease included 21 percent of all women with dense breasts.

Interval cancer rates were not considered high in women with a BCSC five-year risk of less than 1.66 percent even if they had heterogeneously dense or extremely dense breasts.

“Breast density should not be the sole criterion for identifying women who should receive counseling about supplemental imaging,” wrote the authors. “Breast cancer risk combined with breast density categories can identify women for whom supplemental imaging discussions are most appropriate.”

The authors added that discussion of alternative screening should consider the effect of breast density on the rate of false-positives, and suggested that the combination of density information and five-year risk could help identify women who would most benefit from tomosynthesis, which has better specificity than digital mammography.

In an accompanying editorial, Nancy C. Dolan, MD, and Mita Sanghavi Goel, MD, MPH, of Northwestern University Feinberg School of Medicine in Chicago, praised the work of Kerlikowske and colleagues as “compelling evidence” that breast density alone should not guide supplemental screening decisions.

“Incorporating a risk assessment, such as the BCSC 5-year risk, into the mammography report in addition to breast density information might help clarify risk and improve physicians' ability to effectively counsel patients on appropriateness of supplemental screening,” wrote Dolan and Goel. “In particular, this may assist primary care providers, who are currently ill-prepared to discuss breast density with their patients, even in states that have enacted legislation.”