What is Breast Density?

Breast density is a common occurrence, with 40-50 percent of women in the United States possessing dense breast tissue1. It’s completely normal, especially in younger women, and is not necessarily something to be concerned about. Breast tissue is considered dense when it contains more fibroglandular tissue (tissue made up of fibers like nerves, muscles or glands like milk ducts) relative to fatty tissue. Breast tissue density is not something that can be felt, but can be seen on a woman’s screening mammogram.

After I did my mammogram…they saw a shadow, and because of my breasts being very dense, they recommended that I do an MBI. Next thing I know is I’m being contacted that I’ve got breast cancer…I was scared, but, I’m glad that they were able to find it.Barbara, patient at Baptist Health

Why does breast density matter?
While  breast tissue density in and of itself is not a concern, it may be masking a potential problem. During a mammogram, even on newer 3D tomosynthesis devices, the dense fibroglandular tissue appears white, just as breast cancer does. It’s similar to trying to find a snowflake in a snowstorm. When measured against other imaging modalities like Molecular Breast Imaging (MBI), MRI or even ultrasound, the sensitivity of a mammogram has been reported to be as low as 30% in women with dense breast tissue.1,2,3,4

How is breast tissue density measured or scored?
Mammogram findings and results are described using a standardized system called the Breast Imaging Reporting and Data System (BI-RADS), helping to ensure better and consistent follow up of a suspicious finding. As part of the assessment, breast density is evaluated and ranked on a scale. Women with a BI-RAD score of C or D are considered to have dense breast tissue. Understanding density level is helpful in determining if additional studies should be considered. Learn more about BI-RAD scoring from the American Cancer Society.

    • A = Fatty Breasts: 0-25% dense
    • B = Scattered Fibroglandular Densities: 25-50% dense
    • C = Heterogenously Dense: 50-75% dense
    • D = Extremely Dense: 75-100% dense

In recent years, legislation requiring physicians to inform patients of their breast density has been passed in 27 states to date, and many more states have bills drafted and in process. These laws help ensure that women with dense breast tissue are informed about their breast density and to seek additional medical advice to determine additional diagnostic options. Women should be informed of their breast density as well as secondary screening options. It’s important to understand the limitations of anatomical diagnostic imaging options such as mammography, tomosynthesis, and ultrasound. Alternatively, functional diagnostic imaging options, such as MRI and Molecular Breast Imaging (MBI) have the ability to find cancer in dense breast tissue. Women need to be aware of the increased risk associated with dense breast tissue, to allow them to further advocate for their own health. Learn more about dense breast tissue, legislation and which states require dense breast tissue notification from Are You Dense Advocacy and Dense Breast-Info.

Does breast tissue density increase my risk of breast cancer?
Yes. Not only is there a risk of breast cancer being hidden within dense breast tissue, but your risk of developing breast cancer also increased. Studies have shown that women are more likely to develop cancer if they have dense breast tissue, which is only compounded by the difficulty in finding these cancers with anatomical screening methods such as mammography, tomosynthesis, and ultrasound.

Why should I be concerned with my dense breast tissue?
It’s important to speak with your doctor regarding your breast tissue density score, and the risk that it may put you at. Dense breast tissue may be masking tumors 6 which can result in:

  1. Delay in breast cancer diagnosis6
  2. Worsened prognosis7,8
  3. Limited surgical options (reduction of the use of breast conserving surgery, i.e. more mastectomies9)
  4. and even death.7

Your doctor may recommend additional screenings such as Molecular Breast Imaging to Be Certain that nothing has been missed. In a peer-reviewed journal article that reviewed patients diagnosed with cancer, 71 percent were categorized as being dense breast patients (BI-RADS C, heterogeneously or BI-RADS D, extremely dense)10. For this reason, it’s important to understand your density and complete secondary screenings to ensure that if cancer is evident, it’s diagnosed as early as possible when there may be more treatment options and a better prognosis. Alternatively, your doctor may suggest other secondary diagnostic methods such as an ultrasound, tomosynthesis (3D mammography), or an MRI. Learn more about dense breast tissue from the Mayo Clinic.

Opinion Leader Quotes

Robin Shermis, MD, MPH, FACR
Robin Shermis MD, MPH, FACR
ProMedica Breast Care
It’s important for women to know that if they have a dense mammogram…she needs more than just a traditional mammogram, she needs to go on to MBI or MRI.

James Kinsella, MD
James Kinsella MD
Marshfield Clinic
No longer forced to use a ‘one size fits all’ approach for breast cancer detection, our imaging protocol will now be personalized.  The specific needs of each woman will be matched to the imaging technology best suited to her. This will benefit women as well as their health care providers, allowing a well-informed, cutting-edge and shared decision-making environment.

Christine Granfield, MD
Christine Granfield MD
Baptist Health
It's important that we do additional imaging in any woman with dense breasts because there is an increased risk of developing an additional breast cancer in the involved breast or the opposite breast.

1Mandelson MT, et al. J Natl Cancer Inst. 2000; 92: 1081-7

2Berg WA, et al. JAMA. 2012; 307(13): 1394-1404

3Pisano ED, et al. Radiology. 2008; 246: 376–383

4Rhodes DJ, et al. Radiology. 2011;258(1):106-118.

5Boyd NF, Guo H, Martin LJ, et al. Mammographic density and the risk and detection of breast cancer. N Engl J Med. 356(3):227-36, 2007.

6Kolb TM, et al. Radiology. 2002; 225: 165-175.

7Chiu SY-H, et al. Cancer Epidemiol Biomarkers Prev. 2010; 19:1219–1228.

8American Cancer Society. Breast cancer survival rates by stage.

9Arora N, et al. Annals of Surgical Oncology 2010; 17S:211-18.

10Arora N, King TA, Jacks LM, et al. Impact of Breast Density on the Presenting Features of Malignancy. Ann Surg Oncol. 2010;17(3):211-218. doi:10.1245/s10434-010-1237-3