Research shows that the sensitivity of mammography is reduced by up to 20% in women with dense breasts and that breast density is the strongest predictor of the failure of mammograms to predict breast cancer. This occurs because dense breasts—those containing a higher ratio of fibroglandular tissue to fat—can obscure or mask a cancer (Figure).
The phenomena of masking prompted initial legislation in Connecticut mandating that breast density be reported to both patients and providers. To date, 12 states have passed breast density laws (Table). In short, this legislation requires facilities to notify women with dense breasts in writing, alerting them that the condition can interfere with the effectiveness of a screening mammogram. These notifications may also give patients advice about discussing screening options with their primary physician and report that dense breast tissue may be an independent risk factor for breast cancer.
|Figure. Normal dense breast tissue (left) and normal fatty breast tissue (right) are shown. |
(Courtesy of Dr. Dwight Kaufman, National Cancer Institute.)
Some believe that this legislation ensures that all women who undergo a mammogram will receive critical breast-health information. But there is a downside, according to the California Breast Density Information Group (CBDIG), a group of breast radiologists and breast cancer risk specialists representing academic and community-based practices in California.
|US States With Breast Density Laws|
|State||Effective Date||Insurance Mandate|
|New York||Jan 2013||No|
|North Carolina||Jan 2014||No|
|*Amended July 2013 to underscore that dense breast tissue may be associated with an increased risk of breast cancer.|
Many of the laws broadly classify breast density and don’t account for the varying levels of risk among patients with different breast densities. The CBDIG explains: When risk is expressed relative to average breast density, the risk for the 40% of women with heterogeneously dense breasts is about 1.2 times greater than average and the risk for the 10% of women with extremely dense breasts is about 2.1 times greater than average. Therefore, breast density is a risk factor, but not a strong one.
Another problem is that the Breast Imaging-Reporting and Data System (BI-RADS) composition classification system is quite subjective. Breasts in category 1 are considered the fattiest, whereas breasts categorized as 4 are the densest. Category 1 and category 4 breasts may be easy to classify, but breast tissue in the middle categories may sometimes be classified as “2” and at other times “3” depending on the day, according to observational studies.