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Breast Density: What You Need to Know

Breast density refers to the relative amount of glandular and fibrous tissue that each woman has in her breasts compared with the amount of fatty tissue present. Each woman has a different breast density. You cannot know your breast density by a physical exam, it is only determined on a mammogram. Women with mostly fatty tissue do not have dense breasts and women with more fibrous or glandular tissue have dense breasts. Dense breasts are normal (not a disease) and are found in 40-50% of women.

Dense breasts appear more white on mammography. Because cancers usually appear white on mammograms, they are more difficult to detect the more white the mammogram appears.

Breast density is the most common reason for missing a cancer on a mammogram and women with dense breast tissue are also at slightly increased risk for breast cancer. Mammograms are still good at detecting breast cancer but the denser your breasts are, the less accurate they will be at detecting breast cancer.

Breast Density Image

How Does Breast Density Affect Your Health?

All women should have a discussion with their health care provider about their lifetime risk for breast cancer. If your lifetime risk for breast cancer is over 20%, you should have an MRI to supplement your annual mammogram, even if your breasts are not dense.

If your lifetime risk of breast cancer is less than 20%, you should know that 3D mammography improves cancer detection in all breast densities but especially for women with heterogeneously dense breasts. We recommend that all women consider having 3D mammography.

1 in 8 women will develop breast cancer over the course of their lifetime so the average women's lifetime risk of breast cancer is 12-13%.

Breast Density Image

If you have dense breasts and other risk factors for breast cancer, discuss your risk and density with your doctor. This will help guide discussions about screening and which tests might be right for you. Screening decisions should take into account your values and philosophy.

There are no medical guidelines for additional screening for women with dense breasts but some women may prefer to add additional testing to help detect breast cancer. Each additional test may add additional cost, anxiety and chances to detect abnormalities that are not cancer (false positives). It is therefore a personal decision about how much you are willing to do for the chance that should you be diagnosed with breast cancer, that it will be detected as early as possible.

Please be aware that some supplementary screenings may not be covered by insurance. So talk with your doctor and check with your insurance company to help you make your decisions on screening. There are no straightforward answers for women with dense breasts.

Screenings could include:

  • Mammogram – A mammogram uses low-level X-ray to detect changes in breast tissue. If you are a woman age 40 or older and in good health, the radiologists who are experts in interpreting breast imaging recommend you have a mammogram every year, as this regimen is proven to detect the most cancers at the earliest stage. Other physicians may recommend different screening regimens, based on a different value placed on the harms of false positives and additional testing. It is a personal decision, that only each women can answer.
  • 3D Mammography (Tomosynthesis) – A 3D Mammogram improves detection further – and has the added advantages of reducing false positive results. It is a good way to improve cancer detection whether or not your breasts are dense. There is no significant additional radiation, there are fewer false positives and most insurance now covers it.
  • Breast Ultrasound – Whole breast ultrasound can be used to supplement mammography screening if you wish to pursue additional testing. Ultrasound detects more small invasive cancers than mammography, but it has a higher false positive rate. Additional cancers may be detected but at a cost of additional follow up testing and biopsies. The risk of having to undergo additional testing does go down after a few years of screening.
  • Breast MRI Breast MRI is usually recommended for women at elevated risk for breast cancer regardless of their breast density (as a supplement to mammography). It is the best test we have to detect cancer in women at high risk.

Helpful Resources and Websites

There are many helpful resources and websites if you would like to learn more information about breast density. We recommend the following:

Why Choose Us

Named a Breast Imaging Center of Excellence by the American College of Radiology, the UVM Medical Center offers specialized expertise and exceeds rigorous standards for breast imaging care. Mammograms are interepreted with a high level of expertise by experienced radiologists who specialize in breast imaging. We have the highest volume of studies in the state and research has documented that quality improves with numbers of studies interpreted.

We can provide for all of your breast imaging needs, including needle biopsies for diagnosis in a patient centered environment where a friend or family member can be present if you wish. We are staffed by a talented and dedicated group of knowledgeable and caring breast imaging radiologists, technologists and sonographers. We definitely try to put the patient first.

Contact Us

For more information call 802-847-2446 or email us with questions at mammoinfoatuvmhealth [dot] org.


Breast Density Information for Health Care Providers

Breast Density Image

Breast density refers to the relative amounts of fatty versus glandular and fibrous breast tissue as seen on mammography. (One cannot assess density by physical exam). Although density is a continuous spectrum, radiologists divide breast density into 4 categories:

  • Almost entirely fatty (10% of population)
  • Scattered fibroglandular (40%)
  • Heterogeneously dense (40%)
  • Extremely dense (10%)

The last two are considered dense and the first two are considered non-dense. Density, on average, decreases with age with up to 70% of women in their 40's having dense breasts and 35-40% of women in their 70's having dense breasts.

Density is also affected by changes in body weight. Radiologists' assignment of density category is subjective and there is considerable inter-and intra-observer variability in the center of the spectrum (between scattered and heterogeneously dense) but much less variation at the two ends of the spectrum. So it is possible that some patients' density assessment category may change from year to year.

Breast Density Images

Masking Effect and Risk

While mammographic sensitivity is 98% in women with fatty breasts, the higher the density, the lower the sensitivity; with only 36-60% sensitivity in women with heterogeneously dense and extremely dense breasts. This is known as the “masking effect” of dense breast tissue. Besides being the number one cause of a missed cancer on mammography, breast density also imparts a higher risk for breast cancer. Those with heterogeneously dense breasts have 1.3-1.5 x the risk of those with scattered fibroglandular tissue and those with extremely dense breasts have 2.1-2.3 x the risk of the average woman. 

Screening mammography has been proven to reduce the risk of death from breast cancer. All screening decisions need to balance the benefits of early detection and the potential harms of false positives and possible over-detection. This balance can only be achieved by considering patient values and preference.

Screening Mammography 

Women with dense breasts may wish to supplement mammography with other testing in order to minimize the chance of a missed cancer on mammography and prevent diagnosis of cancer at an advanced stage. There are no current medical society guidelines or best practices in choosing who would benefit from supplementary screening in addition to mammography. There is growing consensus that those with extremely dense tissue would benefit from added testing. Each additional screening modality that is added to mammography has an increased risk of false positives and of over-diagnosis. Providers will need to be familiar with strengths and weaknesses of the available supplementary screening modalities.

You can see all the available supplementary technologies for breast cancer screening and their relative pros (increased cancer detection) and cons (false positives and radiation or contrast risks) at Dense Breast Info.

The following supplementary screening modalities are available at the University of Vermont Medical Center:

Counseling Patients

The first step in patient counseling is risk assessment. Risk assessment is important for all patients; dense or non-dense. Women with greater than 20% lifetime risk according to risk models that rely primarily on family history (for example Tyrer Cuzik, Claus or BRCAPRO) should have mammography supplemented with annual MRI. (American Cancer Society Guidelines for Breast Screening with MRI as an Adjunct to Mammography).

For women with average risk and non-dense breasts, annual mammography beginning at 40, 3D preferably, would be sufficient.Those with extremely dense breasts should consider supplementing mammography with ultrasound or MRI. Those with heterogeneously dense breasts might consider supplementary screening if they have other risk factors for breast cancer besides density or if there is a strong personal preference/drive for early detection.

There are several resources you can use to help guide discussions with patients about how to best screen and whether or not to supplement mammography with alternative screening methods.

At the UVM Medical Center, we generally perform 3D mammography for screening on most patients (except those that decline due to payment issues). As we use synthesized 2D in addition to 3D, there is no longer significantly increased radiation dose. 3D mammography has a lower false positive rate and higher cancer detection rate than 2D alone. A recent study showed this was true for all breast densities but adding 3D resulted in the most significant improvement for heterogeneously dense breasts with much less of an improvement in extremely dense breasts. (Breast Cancer Screening Using Tomosynthesis and Digital Mammography in Dense and Nondense Breasts).

Insurance Coverage

Supplementary screening in addition to mammography will be covered by insurance to a variable degree. All supplementary screening is now covered in New York State by law and several other states are introducing legislation to that effect. In Vermont we have had increasing success in insurers covering 3D mammography but there are still some who do not. Coverage of supplementary ultrasound screening would be at the discretion of the insurer currently.

Resources For Dense Breasts

Additional Resources:

  1. Mammographic Breast Density: Effect on Imaging and Breast Cancer Risk - Renee W. Pinsky, MD; Mark A. Helvie, MD.
  2. Breast cancer screening in the era of density notification legislation: Summary of 2014 Massachusetts experience and suggestion of an evidence-based management algorithm by multi-disciplinary expert panel. Freer et al, Breast Cancer Res Treat. 2015 Sep;153(2):455-64. doi: 10.1007/s10549-015-3534-9. Epub 2015 Aug 20.
  3. Identifying Women With Dense Breasts at High Risk for Interval Cancer: A Cohort Study; Kerlikowske et al; Ann Intern Med. 2015;162(10):673-681. doi:10.7326/M14-1465
  4. Breast Density and Breast Cancer Risk: A Practical Review; Wang et al; Mayo Clinic Proceedings, 2014-04-01, Volume 89, Issue 4, Pages 548-557
  5. Mammographic Density and the Risk and Detection of Breast Cancer; Boyd et al, N Engl J Med 2007; 356:227-236, January 18, 2007,DOI: 10.1056/NEJMoa062790
  6. Mammographic Breast Density: Impact on Breast Cancer Risk and Implications for Screening, Phoebe E. Freer, RadioGraphics, 2015, 35, 2, 302, DOI.
  7. Opinion Piece: Viewpoint, The divide between breast density notification laws and evidence based guidelines for breast cancer screening: Legislating practice; Haas and Kaplan, JAMAintmed, July 2015
  8. Assessing Improvement in Detection of Breast Cancer with Three-dimensional Automated Breast US in Women with Dense Breast Tissue: The SomoInsight Study;  Brem et al, Radiology, vol 274, issue 3, DOI.
  9. Benefits, harms, and cost-effectiveness of supplemental ultrasonography screening for women with dense breasts. Sprague BL, Stout NK, Schechter C et al (2014) Ann Int Med. doi.
  10. Current Status of Supplemental Screening in Dense Breasts, Commentary by Dr. Wendie Berg on the ASTOUND trial (reference below), Published online before print March 9, 2016, doi: 10.1200/JCO.2015.65.8674 JCO March 9, 2016 JCO658674.
  11. Adjunct screening with tomosynthesis or ultrasound in mammography-negative dense breasts (ASTOUND): Interim report of a prospective comparative trial. Tagliafico AS, Calabrese M, Mariscotti G, et al. J Clin Oncol, doi.
  12. Variation in Mammographic Breast Density Assessments Among Radiologists in Clinical Practice: A Multicenter Observational Study. Sprague et al; 2016 Ann. Intern. Med. Published online 19 July 2016
  13. Supplemental Screening for Breast Cancer in Women With Dense Breasts: A Systematic Review for the U.S. Preventive Services Task, Melnikow, et al, Ann. Intern. Med.2016;164(4):268-278. doi:10.7326/M15-1789.
  14. McDonald ES, Oustimov A, Weinstein SP, Synnestvedt MB, Schnall M, Conant EF. Effectiveness of Digital Breast Tomosynthesis Compared With Digital Mammography: Outcomes Analysis From 3 Years of Breast Cancer Screening. JAMA Oncol 2016. doi: 10.1001/jamaoncol.2015.5536
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