Women with Extremely Dense Breasts Benefit Less from 3D Mammography

Most women will have better cancer detection and face fewer recall visits due to unclear findings if they undergo digital breast tomosynthesis (DBT) instead of digital mammography, according to a new study. But, not all women experience the same benefit.

In a study published July 28 in JAMA Network Open, investigators from the University of Washington School of Medicine detailed the superiority of DBT, as well as the reasons why it does not work the same for all women, raising a concern about undetected and untreated cancers.

“DBT is improving screening outcomes for the vast majority of women getting screening mammography,” said co-lead study author Kathryn Lowry, M.D., assistant professor of radiology at the University of Washington. “Unfortunately, it does not seem to benefit the 10 percent of women who have extremely dense breasts and who already experience the poorest of mammography outcomes today.”

Within the past decade, DBT has gained a reputation for providing better cancer detection – an outcome that has reduced the number of follow-up calls many women face with breast cancer screening. Still, to date, there is a lack of research into the performance differences between various sub-groups of women. To pinpoint those differences, Lowry’s team evaluated more than 1.5 million breast exams – 1.27 digital mammography and 310,000 DBT – from women between the ages of 40 and 79 from 46 sites between January 2010 and April 2018. These women had no prior breast cancer, mastectomy, or breast augmentation history. Not only did the team measure the detected cancers, but they also examined recall rates by age group, breast densities, and the characteristics of baseline versus subsequent exams.

In addition, she said, the vast amount of data examined was geographically, racially, and ethnically diverse, allowing her team to address previously unexplored questions.

According to the study analysis, the investigators determined that DBT works best for women getting their first screening mammogram. This group experiences both better cancer detection and a reduction in recalls. At baseline, the team found that DBT outperformed digital mammography across all ages and breast densities. Of all the cancers detected, 75 percent were invasive.

Baseline Screening Recall Rates

Baseline Cancer Detection Rates per 1,000 Women

Additionally, women who undergo subsequent exams typically enjoy at least one of DBT’s benefits, the team said. DBT recall rates were lower for women with scattered fibroglandular density and heterogeneously dense breasts across all age groups, and women with almost entirely fatty density classifications also had a lower screening recall rate.

But, those benefits do not extend to women with extremely dense breast tissue, Lowry said. This group saw neither a recall rate drop nor better cancer detection.

“This is a concern because this group of women is known to be at higher risk for cancer,” she said, “and higher risk for having cancers missed by mammography.”

Lowry did note, however, that women who were categorized as having dense breast tissue (but not extremely dense) did still realize the benefits of DBT. In fact, they saw the largest improvement in cancer detection.

Alongside the improvements in cancer detection and recall rates, the team also determined that biopsy recommendation rates were higher for DBT than digital mammography for baseline exams across all ages.

On a broader note, Lowry said, the results of this study indicate that breast density should likely not be used as a criterion for triaging DBT for routine screening where it is not already universally available. This is important within the context of state mandates for supplemental breast cancer screening, she said, because women with extremely dense breasts will benefit more from digital mammography than DBT for routine screening.

Ultimately, Lowry said, these results will help both patients and providers make better decisions about screening mammography.

“If a provider only has access to one or two DBT machines, it will help them determine which patients should get priority with those,” she said. “If a patient has to pay more out-of-pocket or drive several hours to reach a provider who offers DBT, this can help them know whether they’re likely to experience benefit.”