Laws requiring notification of dense breasts are well meaning but could pose a risk of unnecessary procedures and false positives for women at low- and moderate-risk of breast cancer, says a new commentary published in the New England Journal of Medicine (2015; 372:593-595).

Women with dense breast tissue are at increased risk of breast cancer. Dense breast tissue, generally defined as having more fibroglandular than fatty tissue, can make it more difficult for radiologists to detect cancer on screening mammography.

Twenty-one states have passed breast density laws ranging from requiring radiologists to notify women of their breast density and that dense breasts may increase their risk for breast cancer to offering supplemental screening with ultrasound for women found to have dense tissue on mammography.

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“Given recent concerns raised by the US Preventive Services Task Force about false positives and increased patient anxiety with even routine mammography screening, widespread supplemental screening for all women with dense breast tissue without careful consideration of the risks and benefits would be unwise,” said lead author Priscilla J. Slanetz, MD, MPH, director of breast imaging research and education at Beth Israel Deaconess Medical Center and an associate professor at Harvard Medical School in Boston, Massachusetts.

The implementation of state laws has varied across states, especially as most laws do not mandate insurance coverage for any of these supplemental screening tests.

Slanetz and colleagues point out that the medical community has been more cautious than the grassroots movement in embracing supplemental screening, noting that the ability to detect breast cancer can be affected by a broader range of factors beyond screening mammography.

Use of any supplemental screening tool should be based on existing evidence, the authors said. Currently, mammography is the only screening tool that has been shown to reduce breast cancer mortality and does so by 15% to 30%.

Supplemental screening with breast MRI for women considered at high-risk of breast cancer, whether or not they have dense tissue, has been shown to be diagnostically effective and cost-effective. However, the authors said there is little evidence to support widespread supplemental screening using ultrasonography for women with dense tissue, even though this has been mandated by some state laws.

In fact, although whole breast ultrasound screening can detect up to three additional cancers in women of above average risk and dense breasts, this test also carries a relatively high risk of false positives, which can lead to increased patient anxiety, higher costs, and unnecessary biopsies.

The authors wrote that these issues, along with growing concerns about overdiagnosis and subsequent overtreatment, emphasize the need to develop better tools that can differentiate between clinically significant and insignificant tumors.

While cancer risk is between 1.2 and 2.1 times higher for a woman with dense breast tissue compared to a woman with average breast density, Slanetz and colleagues noted that there are other important risk factors to consider to determine whether supplemental screening may be indicated. For example, a woman’s risk of breast cancer doubles if she has a first-degree relative who has had or has breast cancer and increases eight-fold if she has a relative who is known to carry a BRCA1 or BRCA2 gene mutation.