Have you ever been told that you have dense breasts? It’s an important piece of information because women who have them are at increased risk for breast cancer…and because mammograms don’t do a very good job of detecting cancer in dense breasts.

That’s why five states (CA, CT, NY, TX, VA) now have laws requiring mammography clinics to inform women if they have dense breasts. Similar legislation is currently being considered in about a dozen other states, as well as in Congress.

No matter where you live, though, if your doctor doesn’t bring up the subject of breast density, you should ask about it, said Margarita Zuley, MD, an associate professor of radiology at the University of Pittsburgh and medical director of breast imaging at Magee-Womens Hospital. Ask, too, whether you need additional screening tests for breast cancer, as many dense-breasted women do…and also discuss the best timing for those tests.

Why it matters: Breasts are made up of ducts, glands, fibrous connective tissue and fatty tissue. Dense breasts have a higher percentage of fibrous and glandular tissues and less fatty tissue. Younger women are most likely to have dense breasts because breasts typically become more fatty with age, but even so, as many as 25% of postmenopausal women have dense breasts. Concern: Women with dense breasts are two to six times more likely to develop breast cancer—perhaps because dense breasts have more milk ducts and lobes, and the majority of breast cancers form in such tissues.

What’s more, tumors are harder to detect in dense breasts because, on a mammogram, dense tissue looks white…and so do cancers. That’s why looking for cancer in a dense breast is like looking for a polar bear in the snow. Fatty tissue looks darker, so it provides more contrast compared with any cancer that might be present. When a radiologist looks at your mammogram and compares it to your mammograms from previous years, he or she is looking for areas that once appeared dark and now look whiter, Dr. Zuley said. If you have dense breasts, little cancers buried between glandular breast tissues can easily go undetected.

The only way to know whether you have dense breasts is by having a mammogram. Your doctor cannot tell just by doing a manual breast exam.


Dense-breasted women still do need regular mammograms because the test does spot some tumors in dense breasts, including ones that other tests miss. However, the best odds of detecting cancer in dense breasts occur when mammography is combined with an additional screening test. If you have dense breasts, discuss these options with your doctor…

Ultrasound. The most commonly used supplemental breast-screening test, ultrasound often picks up cancers in dense-breasted women that mammography misses. It’s also noninvasive, relatively inexpensive (about $100) and doesn’t involve radiation. Dr. Zuley said that ultrasound is generally considered an appropriate add-on test for dense-breasted women who are at average or intermediate risk for breast cancer.

The downside is that ultrasound has a high rate of false-positive results. Dr. Zuley explained that breast ultrasounds reveal a lot of abnormalities, such as fibroadenomas (solid, benign, glandular breast tumors), which must be biopsied to see whether they are cancerous but which ultimately turn out to be benign. False-positives involve unnecessary anxiety, inconvenience and expense. Number crunch: Studies show that, for every 1,000 women screened, the addition of ultrasound spots three to five cancers that mammograms miss…however, to find three tumors, 63 biopsies or other invasive procedures are done.

Magnetic resonance imaging. MRI is better at detecting breast cancer than other screening methods are. However, it is generally used only for women who are at high risk for breast cancer because they carry the breast cancer gene or because one or more of their first-degree relatives (parent, sibling) had the disease.

Why isn’t MRI used for all dense-breasted women? Because compared with ultrasound, breast MRI is much more costly (upwards of $700)…more invasive, as it requires the injection of an intravenous contrast dye…and has an even higher rate of false-positives.

Tomosynthesis (3D mammography). With regular 2D mammography, a single image is taken each time the breast is compressed—which means that tissues overlap and details are obscured. With tomosynthesis, however, the arm of the X-ray machine rotates in an arc above the breast, taking many separate images. Those are then processed on a computer to create a 3D image that the radiologist can manipulate to view 50 to 60 individual millimeter-thin “slices” of breast tissue, making it easier to spot tumors hiding in dense tissue.

Recent studies show that radiologists who had access to both 2D and 3D mammograms detected 40% more cases of invasive breast cancer than those who saw only the 2D mammograms…and that the combination of 2D and 3D images reduced false-positive results by 39%. Due to the 3D test’s higher rate of detection of invasive breast cancer, Dr. Zuley recommends tomosynthesis for all women, whether dense-breasted or not. The 3D scan uses about the same amount of radiation as the 2D scan, so getting both tests doubles your radiation exposure. Still, the total radiation dose for the combined tests is well below three milligray, which is the FDA limit for a single mammogram.


Because tomosynthesis is relatively new, it is currently FDA-approved for use only in addition to, not instead of, regular 2D mammography. So even if your doctor recommends that you get a 3D mammogram, he or she will still tell you that you need the 2D test as well—at least until additional studies lead to FDA approval of tomosynthesis as a stand-alone mammography technique. Since both types of mammograms can be performed on the same equipment in rapid succession, both tests generally are done at the same time.

No matter whether a woman gets just a 2D mammogram or a 3D mammogram as well, if her doctor also wants her to get an ultrasound or MRI, the question of timing arises. That issue is currently being debated in the radiology community.

Some doctors believe it is best for a woman to have her regular annual mammography screening and then, six months later, to have her breast ultrasound or MRI. This way, if she has a fast-growing tumor, it will be detected sooner because she will never go longer than six months before having some kind of imaging test.

However, Dr. Zuley and many other experts prefer to do the annual mammography screening and the ultrasound or MRI on the same day. That’s because the six-month alternating schedule has not been shown to increase detection rates, she said…and because comparing the two test results at the same time helps reduce the rate of false-positives, avoiding a lot of unnecessary anxiety and biopsying of tissues that turn out to be fine.

Some health insurance policies cover the cost of the additional screening tests for dense-breasted women, but some do not—so check with your insurer.

Lots more about breast cancer: For 19 news-filled articles on how to prevent, detect, treat and recover from breast cancer, see our special Breast Cancer Guide.

Source: Margarita Zuley MD, associate professor of radiology, University of Pittsburgh, and medical director of breast imaging, Magee-Womens Hospital, both in Pittsburgh. She also is a fellow of the Society of Breast Imaging, has received grant funding from several public and private sources, is a grant reviewer for the National Institutes of Health, and sits on several committees for the American College of Radiology and the Society of Breast Imaging.