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Digital breast tomosynthesis (DBT) screening supplemented by MRI for women with dense breasts led to both greater benefits and increased harms in a model-based comparative effectiveness analysis.

Adding MRI to biennial DBT screening for women ages 50 to 74 years with extremely dense breasts increased deaths averted per 1,000 women over DBT screening alone (7.6 vs 7.4), but also increased false-positive recalls (919 vs 884) and false-positive biopsy recommendations (180 vs 151), reported Natasha K. Stout, PhD, of Harvard Medical School and Harvard Pilgrim Health Care Institute in Boston, and colleagues in .

Extending the use of supplemental MRI to all women with heterogeneously or extremely dense breasts starting at age 50 resulted in 8.0 deaths averted per 1,000 women screened, as well as 1,088 false-positive recalls and 343 false-positive biopsy recommendations.

For women who began screening at age 40, this strategy averted 9.5 deaths per 1,000 women, but led to 1,850 false-positive recalls and 628 false-positive biopsy recommendations.

"Results of this model-based comparative effectiveness analysis provide clinicians and policymakers additional population-level outcomes for informing decision-making about breast cancer screening by breast density," Stout and colleagues wrote. "The balance of this trade-off for supplemental MRI use was more favorable when MRI was targeted to women with extremely dense breasts who comprise approximately 10% of the population and warrants consideration."

"Use of supplemental MRI only among those women with extremely dense breasts may provide a better balance of benefits and harms and could be considered for population-based screening," they noted.

In explaining the rationale for the study, Stout and colleagues said that, starting in September, the FDA will require that all women undergoing mammography be notified of the density of their breasts. In addition, DBT and MRI have been proposed as screening modalities that can of digital mammography, particularly in the case of women with dense breasts.

"With this new national notification requirement, policymakers and healthcare professionals need information on the benefits and harms of screening modalities by extent of breast density," they wrote.

In a , Ilana B. Richman, MD, MHS, and Tracy A. Battaglia, MD, MPH, both of the Yale School of Medicine in New Haven, Connecticut, cautioned that this was a modeling study and long-term follow-up of empirical studies is needed.

"Despite the caveats of modeling, there are 2 important ways in which findings from the study by Stout and colleagues are immediately useful for patient and clinician decision-making," they noted.

For example, they pointed out that the study identified suboptimal screening strategies that should be avoided.

"In particular, annual screening with supplemental MRI and DBT rather than biennial screening with these modalities would produce essentially no additional reduction in cumulative breast cancer deaths and would double the rate of false-positive screens, regardless of breast density category," they wrote, adding that even with the uncertainties inherent in modeling, "these data provide a sense of the absolute benefits and harms of MRI and can be a useful starting place for shared decision-making with patients."

For this analysis, Stout and colleagues used three Cancer Intervention and Surveillance Modeling Network breast cancer simulation models informed by U.S. Breast Cancer Surveillance Consortium data, and examined 60 screening strategies that varied by mammography type, with or without MRI, by the extent of breast density, age of screening initiation, and screening interval. They included simulated women born in 1980 with average breast cancer risk.

Breast density was categorized using the American College of Radiology Breast Imaging Reporting and Data System, with almost entirely fatty and scattered fibroglandular densities referred to as non-dense, and heterogeneously dense or extremely dense breasts referred to as dense.

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