If you’re a woman, you may have dense breasts and not know it. Regardless of their shape and size, dense breasts are an independent risk factor for breast cancer, and women who have them are at least three times as likely to develop the disease as women with nondense (fatty) breasts. The greater the density, the greater the risk.
Only a mammogram can determine if you have dense breasts. You can’t tell by looking at your breasts or feeling them.
But even if you’ve had mammograms year after year, you may still be unsure whether or not you have dense breasts, because your doctor may simply not have told you. That is changing. More than a dozen states—including California, Connecticut, New York, Texas and Virginia—have passed laws requiring clinics that perform mammograms to tell women if they have dense breasts. Several more states are considering similar legislation, while Congress is contemplating a federal law.
Because dense breast tissue can obscure tumors on a mammogram, thus making the test less useful, the typical advice for women with dense breasts is to have supplemental screening with breast ultrasound. For women with other risk factors, MRI may be recommended.
Additional screening: weighing pros and cons
The new legislation has both fans and critics. The American Society of Breast Disease supports it, believing that if women know their risks, they’ll be able to make better-informed decisions about breast cancer screening recommendations. Women also seem to welcome the idea, at least according to a survey presented at the annual meeting of the Radiological Society of North America, which found that many would be interested in having additional screening if they were told they had dense breasts.
Some research supports additional screening. For example, in a large study from Yale University that was conducted in the first year of the law’s enactment in Connecticut, additional ultrasound screening in women with dense breasts detected 3 cancers per 1,000 women— cancers that were missed on mammograms.
And a study published in the Journal of the American Medical Association in 2012 found that ultrasound, done after an annual mammogram, significantly increased detection of invasive breast cancer among women who had dense breasts and at least one additional risk factor for breast cancer, such as family or personal history of the disease. MRIs also detected additional cancers.
Critics, however, point out that ultrasound— and especially MRIs—have high rates of false positives, meaning that they frequently identify spots that look suspicious but are not cancerous. The new laws will thus subject more women to followup tests and even biopsies that are not medically necessary and that increase anxiety and health-care costs. In the recent Yale study, when biopsies were done in women with dense breasts, 94 percent found there was no cancer.
Other concerns: There are currently no standardized methods in clinical practice for determining density on a mammogram; results of standard ultrasound screening depend on the experience of the technician; and the contrast dye used in breast MRIs can provoke allergies in some women. And some people simply don’t want their health care mandated by a law.
Perhaps most important, no one knows if supplemental screening of dense breasts actually saves lives. As recent studies have found, breast density may not even be associated with increased breast cancer mortality.
For example, a 2012 study from the National Cancer Institute found that women with dense breasts who developed breast cancer were not at higher risk of dying from the disease than women with nondense breasts. “Risk factors for the development of breast cancer may not necessarily be the same as factors influencing the risk of death from breast cancer once it has developed,” the researchers said. Another 2012 study, in Breast Cancer Research and Treatment, similarly found that among Caucasian and African-American women with breast cancer, having dense breasts did not affect mortality rates.
Bottom line: Though some questions remain about the benefits of additional screening, we support notification of women if they have dense breasts. If you don’t live in a state that requires this, ask your health care provider at your next mammogram appointment whether you have dense breasts. If you do, other tests in addition to mammograms and a yearly clinical breast exam may be recommended, especially if you have had breast cancer or a breast biopsy, have a strong family history of breast cancer (notably a close relative diagnosed before menopause) or have some combination of risk factors.