Background: Breast density is well recognized as an independent risk factor for the development of breast cancer. However, the magnitude of risk is controversial. As the public becomes increasingly aware of breast density as a risk factor, legislation and notification laws in relation to breast density have become common throughout the United States. Awareness of breast density as a risk factor for breast cancer presents new challenges for the clinician in the approach to the management and screening of women with dense breasts.

Methods: The evidence and controversy surrounding breast density as a risk factor for the development of breast cancer are discussed. Common supplemental screening modalities for breast cancer are also discussed, including tomosynthesis, ultrasonography, and magnetic resonance imaging. A management strategy for screening women with dense breasts is also presented.

Results: The American College of Radiology recognizes breast density as a controversial risk factor for breast cancer, whereas the American Congress of Obstetricians and Gynecologists recognizes breast density as a modest risk factor. Neither organization recommends the routine use of supplemental screening in women with dense breasts without considering additional patient-related risk factors.

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Conclusions: Breast density is a poorly understood and controversial risk factor for the development of breast cancer. Mammography is a screening modality proven to reduce breast cancer-related mortality rates and is the single most appropriate tool for population-based screening. Use of supplemental screening modalities should be tailored to individual risk assessment.


Breast density is an independent risk factor for the development of breast cancer, although the magnitude of this risk is controversial. Breast density is a visual assessment of the ratio of parenchyma to fat as seen on mammography. Fibroglandular tissue is radiodense or white on mammography, whereas fat is radiolucent or black. Four categories of breast density have been defined by the criteria of the American College of Radiology’s (ACR) Breast Imaging Reporting and Data System, 5th ed. (BI-RADS; Figure 1)1:

  • Almost entirely fatty
  • Scattered fibroglandular densities
  • Heterogeneously dense
  • Extremely dense

The sensitivity of mammography for noncalcified lesions decreases as breast density increases due to a “masking” of the lesion by overlying normal tissue.1 Approximately 50% of women have breast tissue classified as either heterogeneously dense or extremely dense, thus reducing the sensitivity rate of mammography.2 However, almost entirely fatty breasts may have coalescent areas of dense tissue that can obscure lesions. Therefore, the BI-RADS criteria allow for the overall assessment of breast density to convey the likelihood of having an obscured lesion or “masking” effect.1 Dense tissue is most often seen in the breasts of younger premenopausal women, but it has also been observed in older postmenopausal women.3