Dense breasts have less fatty tissue and more non-fatty tissue compared to breasts that aren't dense. Dense breasts have more gland tissue that makes and drains milk and supportive tissue (also called stroma) that surrounds the gland. Breast density can be inherited, so if your mother has dense breasts, it's likely you will, too.
One way to measure breast density is the thickness of tissue on a mammogram.
The Breast Imaging Reporting and Database Systems, or BI-RADS, which reports the findings of mammograms, also includes an assessment of breast density. BI-RADS classifies breast density into four groups:
- Mostly fatty: The breasts are made up of mostly fat and contain little fibrous and glandular tissue. This means the mammogram would likely show anything that was abnormal.
- Scattered density: The breasts have quite a bit of fat, but there are a few areas of fibrous and glandular tissue.
- Consistent density: The breasts have many areas of fibrous and glandular tissue that are evenly distributed through the breasts. This can make it hard to see small masses in the breast.
- Extremely dense: The breasts have a lot of fibrous and glandular tissue. This may make it hard to see a cancer on a mammogram because the cancer can blend in with the normal tissue.
Still, no one method of measuring breast density has been agreed upon by doctors. Breast density is not based on how your breasts feel during your self-exam or your doctor's physical exam.
Research has shown that dense breasts:
- can be twice as likely to develop cancer as nondense breasts
- can make it harder for mammograms to detect breast cancer; breast cancers (which look white like breast gland tissue) are easier to see on a mammogram when they're surrounded by fatty tissue (which looks dark)
Steps you can take
If you have dense breasts, there lifestyle choices you can make to keep your breast cancer risk as low as it can be:
- maintaining a healthy weight
- exercising regularly
- limiting alcohol
- eating nutritious food
- never smoking (or quitting if you do smoke)
These are just a few of the steps you can take. Review the links on the left side of this page for more options.
Along with lifestyle options, many doctors recommend additional screening for women with dense breasts. This might include MRI scanning and ultrasound.
More frequent screening: If you have a higher risk of breast cancer because you have dense breasts, you and your doctor will develop a screening plan tailored to your unique situation. General recommended screening guidelines include:
- a monthly breast self-exam
- a yearly breast exam by your doctor
- a digital mammogram every year starting at age 40
Digital mammography is better than film mammography in women with dense breasts, regardless of age.
Your personal screening plan also may include the following tests to detect any cancer as early as possible:
Talk to your doctor about developing a specialized program for early detection that meets your individual needs and gives you peace of mind.
To improve the information learned from your breast imaging studies, it's important to both compare this year's study to prior years' studies and to correlate the information learned from the various imaging studies obtained (what you feel in the breast, compared to the results of your mammogram, MRI, and ultrasound). Usually test reports will say if the recent imaging test is different from other tests or prior results of the same test. Obtaining a copy of each breast imaging report and putting them in a binder keeps you in the loop and reduces the risk of your tests falling through the cracks or someone missing an important finding.
- Increase in risk conferred by having dense breasts. Raghavendra A., et al. Mammographic breast density is associated with the development of contralateral breast cancer. Cancer, 123: 1935-1940. Available at: https://onlinelibrary.wiley.com/doi/full/10.1002/cncr.30573
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