January 7, 2019

Learning you have dense breasts can prompt many questions, including how this affects your risk of breast cancer.


Many women have “dense” breasts. Mary E. Egger, ADN, BSN, MSN, an advanced practice nurse for the Vanderbilt Breast Center’s High Risk Clinic, explains what this means and how breast density relates to your chances of developing breast cancer.


What does the term “breast density” mean?

Breasts are made mostly of fat and glandular tissue. On a mammogram image, fat appears black, and density appears white. Breast density is a measure used when evaluating a mammogram image to describe the proportion of fat to fibroglandular tissue. The greater the amount of fibroglandular tissue, the whiter the mammogram appears, indicating more density.

Radiologists use a scoring system to specify the amount of density in a mammogram, breaking it into four categories:

1. Almost entirely fatty.

2. Scattered amounts of fibroglandular tissue.

3. Heterogeneously dense.

4. Extremely dense.

The first two categories are considered non-dense and latter two categories, dense.


Can you tell if you have dense breasts from a self-exam?

Density may or may not be obvious with a breast exam. Breasts can feel very nodular or dense but not look dense on a mammogram. Imaging (a mammogram) is the best way to determine density.


Are there problems associated with having dense breasts? Is your risk of breast cancer higher?

Because breast density appears white on a mammogram, as do many cancers, it can possibly mask a developing cancer. But dense breasts alone do not increase the risk of breast cancer.

A woman’s risk for breast cancer can be calculated by using an assessment tool based on a risk model. There are several tools available that take different personal traits into account to calculate risk. They all take into consideration family history of breast cancer and ages of family members at the time of diagnosis. Some tools also look at other factors such as breast density, exposure to hormones, family history of genetic mutations that may increase breast cancer risk and personal history of breast biopsies. The risk-assessment tools calculate risk to determine whether you may benefit from genetic testing, risk-reducing medications or other imaging tools in addition to screening mammogram to image the breasts.

In the U.S., a woman has a 1 in 8 (12.4 percent) chance of developing breast cancer in her lifetime. Average risk means a less than 12 percent lifetime risk (a woman’s estimated risk for developing breast cancer over her lifetime or to age 85-90); high risk is greater than a 20 percent lifetime risk; and intermediate risk is a 13 to 20 percent lifetime risk.

Having dense breasts alone does not automatically place a woman at intermediate or high risk for breast cancer.


Why do some women have more breast density than others? Is it genetics or can you change your breast density with lifestyle changes, like dietary or smoking habits?

These are the factors that contribute to breast density:

  • Age: Breast density is generally greater in younger women.
  • Menstrual cycle changes: Density is greater during the luteal phase of menstrual cycle. It is better to have a mammogram first or second week after menstrual cycle.
  • Hormone use: Use of postmenopausal hormones can contribute to increased density that shows on a mammogram.
  • Body build: Thinner women tend to have more dense breast tissue, and obese women tend to have less dense tissue because more of their breast tissue has been replaced with fatty tissue.

How do dense breasts affect mammograms? Should your mammograms use particular technology or imaging? Should you have more frequent mammograms?

The annual screening mammogram remains the standard of care for early detection of breast cancer. Women with dense breasts should undergo a screening mammogram once a year until their life expectancy is less than five to seven years.

There are other imaging options that can be done in addition to a mammogram:

Breast tomosynthesis (“3D mammogram”): An advanced form of mammography that uses low-dose X-rays and computer reconstructions to create three-dimensional images of the breasts.

Advantages: This type of imaging can be helpful in women with heterogeneously dense breasts. Studies have shown that taking breast density into account, supplemental digital breast tomosynthesis led to an increase in the cancer detection rate and in a reduction in the recall rate for women with dense or non-dense breasts.

Disadvantages: This may not be covered by some insurance.


Screening whole-breast ultrasound: Performing an ultrasound of the entire breast can be used with mammography to check the breast for cancer that cannot be felt on physical examination or cannot be seen with a regular mammogram.

Advantages: The whole-breast ultrasound is designed to improve the detection rate of breast cancer in women with dense breasts, beyond what a mammogram alone can find.

Disadvantages: Whole breast ultrasound has been found to have a high false-positive rate, increasing the number of unnecessary biopsies with little gain in detecting breast cancer. It may not be covered by insurance.


Breast MRI: Magnetic resonance imaging is sensitive imaging that uses radio waves and magnets to image the breasts. It is not used for screening purposes alone because it may not detect cancers that a mammogram would detect. It is used to further evaluate known cancers in preparation for surgery and in conjunction with a mammogram in high-risk women to screen for breast cancer.

Advantages: MRI is very sensitive and not limited by dense breast tissue. There is no exposure to radiation.

Disadvantages: Because it is very sensitive, MRI can lead to false positives — things revealed by the MRI that may be biopsied but are not cancers. MRI is a costly test, more expensive than any other breast imaging test. The test is lengthy and positioning may be uncomfortable for some women.


Does breastfeeding affect the density of a woman’s breasts? What about augmentation or reduction?

During breastfeeding, breasts are extremely dense. A history of breastfeeding does not affect density, neither does breast augmentation or breast-reduction surgery.


Is there anything women with dense breasts should do to take special care of their breast health?

Have a screening mammogram annually, and consider tomosynthesis as well as your mammogram. If you have dense breasts combined with other risk factors for breast cancer, consider going to a high risk clinic for your care. If you have extremely dense breast tissue, consider whole-breast ultrasound as an additional screening. For women at high risk for breast cancer (greater than a 20 percent lifetime risk) regardless of breast density, know you have the option of annual breast MRI.




The Vanderbilt Breast Center offers a High-Risk Clinic to help women understand their personal risk of breast cancer. Call 615-322-2064, or click here for more information.