Abstract and Introduction
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. 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):
Right mediolateral oblique views on mammography of the right breast depicting the 4 categories of breast density, as defined by the ACR BI-RADS: (A) almost entirely fatty, (B) scattered fibroglandular densities, (C) heterogeneously dense, and (D) extremely dense. ACR = American College of Radiology, BI-RADS = Breast Imaging Reporting and Data System, 5th ed. Data from reference 1.
Almost entirely fatty
Scattered fibroglandular densities
The sensitivity of mammography for noncalcified lesions decreases as breast density increases due to a "masking" of the lesion by overlying normal tissue. Approximately 50% of women have breast tissue clas sified as either heterogeneously dense or extremely dense, thus reducing the sensitivity rate of mammography. However, a lmost 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. Dense tissue is most often seen in the breasts of younger premenopausal women, but it has also been observed in older postmenopausal women.
Reduced sensitivity rates of mammography due to masking alone do not explain the increased risk of breast cancer associated with increased breast density. First described in 1976, Wolfe identified breast density as a risk factor for breast cancer, qualitatively evaluating the mammographic appearance of the breast. A direct relationship was reported between progressively dense breast tissue and increasing risk of breast cancer. McCormack et al performed a meta-analysis of 42 studies and found that increased breast density was a strong risk factor for breast cancer independent of other known risk factors but was confounded by age and body mass index. The risk of breast malignancy associated with dense breasts has been reported to be 4- to 6-fold, making it second only to age and BRCA carrier status for highest risk.[3,6] However, critics argue that this assessment of risk is an overestimation. The studies compared extremes (ie, dense breasts to fatty breasts) rather than comparing dense breasts to average-density breasts (between scattered fibroglandular and heterogeneously dense tissue). When the risk for breast cancer is expressed relative to average breast density, the risk decreases to 1.2 to 2.1 times higher than the average for heterogeneously dense or extremely dense breasts, respectively. Thus, breast density may more accurately represent a modest risk factor similar to that for a woman with 1 first-degree relative with unilateral postmenopausal breast cancer.
Awareness is increasing among public and medical communities alike regarding breast density as a risk factor for breast cancer as well as the limitations of mammography in women with dense breasts.[2,7] Thus, in 2009, Connecticut became the first state to mandate patient and referring physician notification of dense breasts, as determined by the interpreting radiologist. Since then, 26 states have enacted similar notification laws, and legislation has been introduced in several other states. Controversy surrounds these notification laws, particularly with regard to how notification relates to additional imaging and reimbursement.
Price et al identified the efficacy, benefits, and harms of supplemental screening tests as key issues. Although notification increases patient awareness, it also increases patient anxiety.[9,10] Conversely, notification may give a false sense of security to women with fatty breasts who receive a negative finding on mammography. Critics also raise concerns that notification will increase demand for additional screening beyond mammography, which could result in additional false-positive findings and increased health care costs. Five states have mandatory insurance coverage for supplemental screening, suggesting that disparities could develop between women who can afford additional screening and those who cannot.[8,10,11] In a study performed in New Jersey after the implementation of legislation directed at notifying women of their breast density — which also mandated health insurance coverage — an increase was seen in patients utilizing screening ultrasonography, thus resulting in an expansion of the ultrasonography department at the New Jersey institution as well as increasing the direct cost for health care insurers of approximately $4.9 million to $9.8 million for a given month.
Thus, as notification laws gain momentum, clinicians may be faced with new challenges in their approach to breast cancer screening in women with dense breasts. In this review, we address the available types of supplemental screening studies, the risks and benefits of each modality, and suggest an imaging approach to managing the imaging of dense breasts.
Cancer Control. 2017;24(2):125-136. © 2017 H. Lee Moffitt Cancer Center and Research Institute, Inc.
Copyright by H. Lee Moffitt Cancer Center & Research Institute. All rights reserved.