You are here:

Why breast density matters

What it means to have dense breasts—and how they can affect your breast cancer risk.

After a routine mammogram, your radiologist or doctor might have told you that you have dense breasts. But what exactly are dense breasts, and how can they affect your breast cancer risk?

Simply put, “Women with dense breasts have more mammary tissue than fatty tissue,” explains Dr. Robyn Birdwell, associate professor of radiology at Harvard Medical School, and section head in the division of breast imaging at Brigham and Women’s Hospital. If more than 50% of your breasts is made up of connective and glandular breast tissue (as opposed to fat), then you have dense breasts. About 40% of women have dense breasts.

Why does the density of your breasts matter? Women with dense breasts have a slightly increased chance of developing breast cancer. And, if you do develop breast cancer, dense breasts can make that cancer harder to spot, because both glandular breast tissue and tumors appear white on a mammogram.

Imagine looking at a snowflake on a black glove. Set against the dark fabric, you can make out some of its crystals in detail. Then, take those same flakes and put them in a bed of snow. Now it becomes difficult to distinguish the flakes from their background. That is the challenge radiologists face when trying to read the mammograms of a woman with dense breasts.


Dense breast tissue (right) shows up white on a mammogram, making it harder for radiologists to spot cancerous tumors.

Getting screened

Doctors don’t always tell their female patients when they have dense breasts. However, that may change. Several states are pushing through new laws requiring doctors to tell women their breast density status and to explain how having dense breasts can affect mammogram results. Five states (California, Connecticut, Texas, Virginia, and New York) already have such laws in place.

A study presented in November 2012 at the Radiological Society of North America meeting found that more than three-quarters of women didn’t know their breast density status, but 95% said they’d want additional screening if they did find out they had dense breasts.

The trouble is, even though breast cancer screening tests have improved over the years, no test can diagnose breast cancer with 100% accuracy, especially in women with dense breasts. “We want a perfect imaging test, and there isn’t one,” Dr. Birdwell says. Undergoing additional screening tests (see “Screening tests for dense breasts”) can also be costly. Currently, only two states (Connecticut and New York) require insurance companies to pay for further testing in women with dense breasts.

Know your risks

Protecting yourself from cancer involves more than knowing your breast density status or having more screening tests. “We need to understand the woman’s risk profile,” says Dr. Birdwell.

Several models are available to help assess your breast cancer risk—including tools you can use yourself online (one is available on the National Cancer Institute’s website: These models calculate your breast cancer risk based on

  • your age

  • your personal and family history of breast cancer

  • your race

  • the ages at which you got your first menstrual period and gave birth to your first child (if you have children)

  • whether you carry either of the breast cancer susceptibility BRCA genes

  • whether you’ve had a breast biopsy.

Talk with your gynecologist or general practitioner about your overall risk of developing breast cancer. Together, you can determine what screening tests you need, how often you should get screened, and what prevention strategies you should be following.

Screening tests for dense breasts

Ultrasound uses high-frequency sound waves to examine the breasts. In September 2012, the FDA approved a new, automated breast ultrasound system specifically for screening dense breasts. This ultrasound automatically scans the entire breast and produces several images within a minute.

Magnetic resonance imaging (MRI) uses magnets and radio waves to visualize the breasts. It’s recommended in conjunction with mammography in women at high risk for breast cancer because they have inherited BRCA gene mutations or were previously treated with radiation therapy for Hodgkin’s disease.

Digital mammography sends x-ray images of the breast directly to a computer, instead of storing them on film. Digital images are easier for the radiologist to manipulate and interpret.

Posted by: Dr.Health

Back to Top