Breast density laws addressed by experts

A website has been developed to help navigate the new challenges posed by breast-density notification laws, according to a recent special report.

While mammography is considered the best single modality for population-based screening, its sensitivity is diminished by up to 20% in patients with dense breasts (breasts with a high ratio of fibroglandular tissue to fat). This reduction in sensitivity is due for the most part to masking, a phenomenon in which surrounding dense breast tissue obscures a cancer on mammography. In response, several states have adopted laws requiring patient and referring-physician notification when the interpreting radiologist determines that the pattern of fibroglandular tissue on a patient's mammogram is considered dense.

In California, mandatory reporting requirements took effect on April 1, 2013. The law requires that patients with dense breast tissue on screening mammography receive notification in writing, with advice on discussing their screening options with their primary physician. The California law has potentially enormous implications, as approximately 50% of women undergoing screening mammography are classified as having either "heterogeneously dense" or "extremely dense" breasts. For California alone, this could mean two million notification letters a year and a significant increase in supplementary screening with MRI and ultrasound.

"The legislation was prompted by breast cancer advocacy groups motivated to educate women regarding the limitations of mammography," said co-author Jafi A. Lipson, MD, assistant professor of radiology at Stanford University School of Medicine in California. The report was published in Radiology (2013; doi:10.1148/radiol.13131217).

The broad classification of breast density under California law does not take into account the varying risk levels among patients with different breast densities. 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.

"While additional screening for women with extremely dense breasts could prove beneficial, supplemental screening of the approximately 40% of California women with heterogeneously dense breasts would result in very substantial additional cost to the healthcare system," Lipson said. "There also is concern that the increased use of supplementary screening will ultimately expose some patients to more harm, in the form of false-positive results, than good."

To help address these challenges, Lipson and colleagues in the California Breast Density Information Group (CBDIG) created an online document to answer frequently asked questions about the efficacy, benefits, and drawbacks of supplementary screening tests. The CBDIG document is available online at, and patient-friendly information can be found at
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