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Dense Breasts: Answers to Commonly Asked Questions

What are dense breasts?

Breasts contain glandular, connective, and fat tissue. Breast density is a term that describes the relative amount of these different types of breast tissue as seen on a mammogram. Dense breasts have relatively high amounts of glandular tissue and fibrous connective tissue and relatively low amounts of fatty breast tissue.

How do I know if I have dense breasts?


How common are dense breasts?


How is breast density categorized?

Doctors use the Breast Imaging Reporting and Data System, called BI-RADS, to group different types of breast density. This system, developed by the American College of Radiology, helps doctors to interpret and report back mammogram findings. Doctors who review mammograms are called radiologists. BI-RADS classifies breast density into four categories, as follows:



Does having dense breast tissue affect a woman’s mammogram?

Dense breast tissue appears white on a mammogram, as do some abnormal breast changes, such as calcifications and tumors. This can make a mammogram harder to read and may make it more difficult to find breast cancer in women with dense breasts. Women with dense breasts may be called back for follow-up tests more often than women with fatty breasts.

Are dense breasts a risk factor for breast cancer?




Should women with dense breasts have additional screening for breast cancer?


Nevertheless, the value of supplemental, or additional, screening tests such as ultrasound or MRI for women with dense breasts is not yet clear, according to the Final Recommendation Statement on Breast Cancer Screening by the United States Preventive Services Task Force. Ongoing clinical trials are evaluating the role of supplemental imaging tests in women with dense breasts. NCI’s Contact Center can tell you about clinical trials and provide tailored clinical trial searches to help you learn more about clinical trials related to breast density and breast cancer screening.

Recent research has suggested that for women with dense breasts, a screening strategy that also takes into account a woman’s risk factors and protective factors may be the best predictor of whether a woman will develop breast cancer after a normal mammogram and before her next scheduled mammogram.


NCI’s PDQ® summary for Breast Cancer Prevention includes a section that lists risk factors and protective factors for breast cancer.


  • What are the findings of my recent mammogram?
  • Are other additional screening or diagnostic tests recommended?
  • What steps can I take to lower my risk of breast cancer?

What are researchers hoping to learn about the relationship between breast density and breast cancer?

Some important questions include:

  • Can imaging tests such as 3-D mammography (breast tomosynthesis), MRI, and ultrasound help provide a clearer picture of breast density?
  • Why do some women with dense breasts go on to develop breast cancer, while others do not? Can biomarkers be identified that help predict whether breast cancer will develop in a woman with dense breasts?
  • Can women reduce their breast density, and potentially their breast cancer risk, by taking medicines or by applying topical agents directly to the breast?

NCI's Division of Cancer Prevention (DCP) supports research on cancer screening and risk factors, including breast density, such as this clinical trial for women with dense breasts.  NCI’s Division of Cancer Epidemiology and Genetics (DCEG) conducts research on risk factors for cancer, as explained in this article that explores the relationship between mammographic breast density and breast cancer