Breast Cancer 101

Breast Density: What Women Need to Know

Breast Density Information

Breast density refers to the amount of fibroglandular tissue present in a woman’s breasts. Dense breasts contain more fibroglandular tissue than fatty tissue, and they can make it more difficult for radiologists to detect breast cancers using mammography alone. In addition, recent research suggests that having dense breasts can increase a woman’s risk for developing breast cancer.

California Breast Density Notification Law

The California Breast Density Notification Law requires medical centers that perform mammography studies to inform women and their physicians if their mammograms reveal dense breast tissue. Approximately one-half of women have dense breast tissue. Women who receive this information may at first find it confusing, but it can help them make better-informed decisions about their breast health.

The written report that women with dense breast tissue receive will contain the following notice:

Your mammogram shows that your breast tissue is dense. Dense breast tissue is common and is not abnormal. However, dense breast tissue can make it harder to evaluate the results of your mammogram and may also be associated with an increased risk of breast cancer.

It is important for women with dense breasts to consider consulting with their physicians to learn about supplemental breast screening in combination with mammography. Breastlink recommends that all women, regardless of their breast density, receive an annual mammogram after they reach the age of 40.

Understanding Breast Density

Breasts consist of three types of tissue: fatty, connective, and glandular. Fatty tissue is made up of fat cells. Connective tissue is made up of fibrous cells that provide shape and support. Glandular tissue is made up of milk glands and milk ducts. Breasts that contain more connective and glandular tissue than fatty tissue are considered dense.

It is a misconception that if a woman’s breasts feel firm, they must be dense. The only way to tell if you have dense breasts is with a mammogram. After examining the image, your radiologist will fit you into one of four categories, according to your breast density.

  • Mostly Fatty Tissue
  • Scattered Fibroglandular Tissue
  • Heterogeneously Dense
  • Extremely Dense

Why Do Some Women Have Dense Breasts?

Breast density is influenced by a number of factors. These things include:

  • Age. Younger women are more likely to have dense breasts and breast density tends to decline with age.
  • Genetics. Research indicates that women whose mothers had dense breasts are more likely to have dense breasts themselves.
  • Weight. Women who are low to normal weight are more likely to have dense breasts than women who are overweight or obese.
  • Hormone Therapy. Women using hormone replacement therapy or hormonal contraceptives, such as the birth control pill, are more likely to have dense breasts.
  • Children. Women who become pregnant before age 24, breastfeed, and have three or more children are less likely to have dense breasts.
  • Medication. Women being treated with hormone medication such as tamoxifen (used to prevent breast cancer) are less likely to have dense breasts.

BI-RADS Breast Density Classification System

The Breast Imaging Reporting and Data System (BI-RADS) is a standardized classification system that radiologists use to report breast density findings. They grade breast density on a scale of 1 to 4. Here is what those grades mean:

  • BI-RADS 1: Breast tissue is almost entirely fat, with less than 25% of the breast composed of glandular tissue.
  • BI-RADS 2: Breast tissue contains scattered fibroglandular densities, with between 25% and 50% of the breast composed of glandular tissue.
  • BI-RADS 3: Breast tissue is heterogeneously dense, with between 51% and 75% of the breast composed of glandular tissue.
  • BI-RADS 4: Breast tissue is extremely dense, with more than 75% of the breast composed of glandular tissue.

Are Dense Breasts a Breast Cancer Risk Factor?

Dense breast tissue has been shown to be a significant risk factor for breast cancer. In fact, dense breast tissue has been associated with up to four times the risk for breast cancer and can be as much as twice as high as the risk associated with having a first-degree relative with breast cancer.

At this time, experts aren’t entirely sure why dense breast tissue is linked to a higher risk for breast cancer. It may be that dense breast tissue has more cells and the presence of more cells can allow for them to develop into abnormal cells.

Another hypothesis is that women who have dense breast tissue also have greater levels of estrogen, which contributes to both the breast density and to the risk of developing breast cancer.

Dense breast tissue also makes it difficult to detect cancer using traditional mammography alone. On a mammogram, dense breast tissue appears white – but so do breast masses and cancers. In contrast, cancers are easier to detect in non-dense breasts because fatty tissue appears black on a mammogram, so the white cancer stands out like a lightbulb against a black background.

What are Other Screening Methods for Dense Breasts?

Mammogram is still the most reliable exam for initial detection and screening for breast cancer. According to experts, screening mammography remains the best examination for early detection of breast malignancy in ALL women. However, for women who have particularly dense breasts, a physician may also choose to order a supplemental screening exam.

Other screening exams, which can be used in addition to mammography (and not instead of) include the following:

  • Breast Ultrasound. Breast ultrasound can be helpful as a supplemental screening tool in certain women.
  • Breast MRI. Breast MRI uses magnetic fields and radio waves to create a detailed cross-section of a woman’s breast tissue without the use of radiation. MRI has historically been reserved for women with a combination of risk factors, such as dense breasts and a very strong family history of breast cancer, and/or a known genetic mutation, such as BRCA1 or BRCA2. However, a recent study showed that Breast MRI was a superior supplemental screening method for women at average risk for breast cancer who have dense breasts. (Supplemental Breast Cancer Screening in Women with Dense Breasts and Negative Mammography: A Systematic Review and Meta-Analysis | Radiology (

It’s important to remember that both of these screening tools are not replacements for mammography. They should be used in conjunction with mammogram.

Breast Cancer Risk Assessment at Breastlink

At Breastlink, we believe knowledge is power. We want to help you better understand your personal risk for developing breast cancer, so that you can make the best lifestyle choices and health care decisions to promote your breast health.

Our comprehensive risk assessment program is designed to provide you knowledge of your personal risk factors and is covered by most insurance plans. Visit our Risk Assessment Program.



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