Why Breast Density Matters

4 min read

By JoAnn Pushkin

I thought I was doing everything right. I never missed my annual mammogram. I did self-exams, ate healthy, and had no known risk factors for breast cancer. Yet, one day I felt a lump. I wasn’t particularly worried. I had recently had a “normal” mammogram, which didn’t detect anything. Then I was sent for a diagnostic mammogram, which also didn’t detect anything. But an ultrasound the same day revealed the heartbreaking news: I had breast cancer. Why didn’t it show on the mammograms? It was then that I was told that I had extremely dense breasts and the not-so-small, not-so-early-stage cancer was hidden by the dense tissue. I had never before been told I had dense breasts, never been told that breast density increased my risk for breast cancer, never been told that breast density greatly reduces the effectiveness of a mammogram, and, unfortunately, never been told that additional screening tools were available which might have detected my cancer at an earlier stage.

Mammography is more effective in detecting cancers in some women than others. For women with dense breasts, cancer often grows unseen on mammography and therefore, additional screening may be needed.

Key Facts:

  • Dense breast tissue is common: 40% of women age 40 and over have dense breasts.
  • Breast density is determined through a woman’s mammogram and described as one of four categories depending on the amount of breast tissue in comparison to fat in the breast.
  • Cancer is four times more likely to develop in women with extremely dense breasts than in women with fatty breasts.
  • Though mammograms find some cancers not seen on other screening tests, in dense breasts, mammograms will miss up to 40% of the cancers present.
  • In dense breasts, other screening tests, such as ultrasound or especially breast MRI, in addition to mammography, substantially increase detection of early-stage breast cancers.

Dense breasts increase both the likelihood of developing breast cancer and the risk of that cancer being missed by mammography.

Dense breast tissue shows up as white on a mammogram, while fatty tissue is dark gray. Unfortunately, cancers also display as white on a mammogram. If there is a lot of dense tissue on a mammogram, a cancer can be “hiding” among the dense tissue. This is true even if the mammogram was done with 3D/tomosynthesis. Looking for a cancer in a dense breast has been compared to looking for a snowball in a blizzard.

In dense breasts, a “normal,” “negative,” or “benign” mammogram does not necessarily mean cancer is not present. No matter how recent your last mammogram, a lump or any changes in your breast should be brought to the attention of your health care provider.

In addition to hiding cancer, breast density is also one of many known risk factors for breast cancer. The greater the density of the breast tissue, the higher the risk for developing breast cancer.

When you have your mammogram, your breast density is rated as one of four categories:

  • Category A – Fatty                                                                                                                       
  • Category B – Scattered areas of fibroglandular density
  • Category C – Heterogeneously dense
  • Category D – Extremely dense

Breasts which are Category C – Heterogeneously dense, or Category D – Extremely dense, are considered to be “dense” breasts.

Generally, this information will be provided to you by your health care provider, who will have received it from the facility that performed your mammogram. It may also be included in the letter you receive after your mammogram is performed. Many states (38 and the District of Columbia), now have laws that require some level of information about breast density be included in the letter women receive after their mammogram. However, the laws vary from state-to-state. To learn the reporting requirements in your state, please see the legislative map on DenseBreast-info.org.

Early detection matters, so be an informed self-advocate. All women should know their breast density and individual risk factors, discuss the benefits and risks of additional screening with their health care professional, and pursue additional screening if appropriate for them, to ensure the earliest stage diagnosis possible.




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Patient Video Series: Let’s Talk About Dense Breasts

JoAnn Pushkin is executive director of DenseBreast-info.org. The website, cited as the “most up-to-date and comprehensive resource” on the topic, is the collaborative effort of world-renowned breast imaging experts and medical reviewers.

Pushkin’s initiative and advocacy served as inspiration for New York State's Breast Density Inform law. On the federal level, she continues to lead efforts for a single national “density” reporting standard through both the introduction of the Federal Breast Density and Mammography Reporting Act, as well as the FDA’s Mammography Quality Standards Act regulatory amendment consideration.

This article is part of WebMD’s contributor program, which lets people and organizations outside of WebMD submit articles for consideration on our site. Have an idea for a submission? Email us at [email protected].