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Annual mammograms are recommended for women age 40 and over to screen for breast cancer. Your radiologist may then notify you if you have “dense breast tissue” (as about half of women do). It’s nothing to worry about, but additional screening tests are recommended because mammograms are less accurate in detecting cancer in women who have dense breasts.

You can’t tell if your breasts are dense simply based on your body type, weight or the size and feel of your breasts. “Dense breast tissue is determined by the way the breast looks on the mammogram, not by how the breasts feel on physical examination,” says Regina Hooley, MD, a Yale Medicine radiologist, who is a breast imaging expert at the Breast Center at Yale Cancer Center and Smilow Cancer Hospital. Women with dense breasts should consider further tests, including ultrasound or magnetic resonance imaging (MRI), depending on breast cancer risk. At Yale Medicine, women who don’t have dense breasts are told this when their mammograms are read, so they don’t have to wonder.

Be sure to contact your insurance company before scheduling a mammogram or additional screenings to check your coverage.

What are dense breasts?

Breasts are made up of a combination of glandular and fatty tissues. They’re considered dense if most of the breast is made up of glandular tissue, and fatty if those tissues are predominant.

“The glandular tissue looks white, while the fatty tissue looks grey or black in a mammogram.  We are always looking for small cancers, which are white spots, so dense breast tissue makes the cancer harder to see,” says Dr. Hooley. Research shows that mammograms can be 80 to 98 percent effective in detecting breast cancer in women with non-dense breast tissue. However, the accuracy of mammography drops dramatically, possibly to as low as 50 percent, for women with dense breast tissue.

How are dense breasts screened for cancer?

The latest mammogram technology is called 3D mammography or tomosynthesis. It allows the radiologist to view the breast in thin "slices" rather than as a whole. This improves the radiologist’s ability to detect breast cancer while also reducing and the number of false alarms. The 3D imaging is performed simultaneously with a 2D mammogram, so the length of the exam does not change. The patient’s experience is the same, too. She stands with her breast pressed against the imaging tool in a private screening area.

“If you have dense breasts, you may want to consider getting an ultrasound as well for extra reassurance. Or, at least talk to your doctor about about the pros and cons of any additional testing,” says Dr. Hooley.

Can breast density change over time?

Yes, there are factors in life that can change breast density. 

Pregnant women may have denser breasts because their glandular tissue proliferates and grows. However, after giving birth and after stopping breast feeding, breasts tend to become less dense. Also, breast density may decrease slightly with every child you have (and breast cancer risk is reduced with each child a woman gives birth to). Changes in weight can also affect breast density. Weight gain may decrease breast density and weight loss may increase breast density. Age may slightly reduce the amount of dense tissue in a woman’s breasts as well, so dense breast tissue is slightly less common after menopause. 

Keep in mind, though, that although these factors in life can change breast density, a woman’s breast density may also remain relatively unchanged throughout life.

Do dense breasts run in families?

"We notice that dense breasts tend to run in families, and there is evidence that density has a genetic link," says Dr. Hooley.

It’s important to keep in mind that if your radiologist says you have dense breast tissue, there is nothing unusual or unhealthy about your breasts. “About 50 percent of all women in the United States have dense breast tissue, and it’s really normal,” Dr. Hooley says. Be aware of your breast tissue type, so you can choose to be more vigilant about screening your breasts with additional tests for signs of cancer.

How would a follow-up ultrasound help women with dense breasts?

We recommend that all woman over the age of 40 with dense breasts get an ultrasound test each year (unless their breast density changes). Ultrasound is good for dense breast tissue because it tends to show cancers as dark, and the glandular tissue as lighter in color. That contrast helps radiologists detect small cancers. 

Numerous studies have shown that with ultrasound, radiologists can detect about three additional cancers per 1,000 women screened. That’s a significant number, since, “with screening mammography, we are detecting about five cancers per 1,000 women screened,” says Dr. Hooley.

If you are at high risk for cancer, your doctor will want you to have both an ultrasound and a mammogram. That’s because ultrasounds do not pick up micro-calcifications (calcium deposits), which can be early signs of breast cancer. Mammograms do a good job of detecting these calcifications.

How would a follow-up breast MRI help women with dense breast tissue?

MRI is a useful screening tool for women who are at very high risk for breast cancer. “MRI is probably the best test we have to detect breast cancer because it is very sensitive,” Dr. Hooley says. However, a breast MRI is more costly compared to a mammogram. It’s also a bit more invasive because it requires the radiologists to inject intravenous contrast dye in order to see the breast tissue.

What determines if a woman is at higher risk for breast cancer and should consider a breast MRI?

Groups of women who are very high risk include:

What advice does Yale Medicine offer women with dense breast tissue?

“The first thing to know is that if you get called back after a screening mammogram, don’t freak out,” says Dr. Hooley. About 10 percent of women who have a screening mammogram are asked to come in for additional testing because of concerns about the density of their breasts or because an abnormality has been spotted. Often, however, no problems are found. 

If a radiologist sees an abnormality in follow up tests, you may need to have a breast biopsy. This simple outpatient procedure is done in the radiology department using imaging guidance to allow  the radiologist to obtain a sample from the right part of the breast. The biopsy is then sent to the pathology lab for diagnosis.

Only about 1 out of 10 women who are recalled require a biopsy.

How does Yale Medicine’s approach to breast cancer screening stand out?

Yale Medicine physicians are able to address all of your needs, from screenings and biopsies to treatments, in one place—the Breast Center. Our breast imaging doctors are recognized leaders in the field who conduct research in order to provide the best possible care for our patients, using the latest technology. By using 3-D mammography in tandem with 2-D mammography, we improve the detection of lesions and reduce false alarms to help patients get a more accurate diagnosis. Tomosynthesis is available at all our locations, except the mobile mammography service. For more information on the Smilow Screening & Prevention Program, click here.