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Treating Breast Cancer Early

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Updated Mammogram Regulations on Breast Density: What They Mean

Medically Reviewed By Elizabeth Berger, MD, MS

Guidelines aim to help you understand the meaning of breast density and aid with early detection and treatment.


Sex and gender exist on spectrums. This article uses “woman” to refer to a person’s sex assigned at birth.

About half Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source  of women ages 40 and older have dense breasts. Density refers to the type of tissue that makes up your breasts, including the following:

  • Fibrous tissue contains collagen fibers that support the structure of your breasts.
  • Glandular tissue is the part that makes milk.
  • Fatty tissue fills out the breasts and gives them shape.

Women with dense breasts have more fibrous and glandular tissue than fatty tissue.

Breast density falls into four categories:

A. almost all fatty tissue

B. scattered areas of fibrous and glandular tissue

C. more of the breast is made from fibrous and glandular tissue

D. extremely dense breasts

Women in the C and D categories have been classified as having dense breasts by the American College of Radiology. The only way to know your breast density is with a mammogram.

What to know about dense breasts

Having dense breasts may increase Trusted Source JAMA Peer reviewed journal Go to source your risk of breast cancer and can make cancer more difficult to find.

The risk of breast cancer is about double Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  in women with dense breasts than women without dense breasts. Researchers don’t know the exact reason for this increased risk. 

Fatty tissue shows up black on a mammogram. Breast cancer appears white, but so does fibrous and glandular tissue. The similarity in color makes breast cancer harder to detect in women with dense breasts.

That may be why mammograms miss cancer in dense breasts up to half the time Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source . A previous study suggested the use of ultrasound testing may improve the detection of breast cancer in dense breasts.

Breast density regulations

The March 2023 regulations by the Food and Drug Administration (FDA) update the Mammography Quality Standards Act (MQSA) of 1992, which set standards for imaging centers to ensure that all women have access to quality mammograms. Having mammograms is essential for early detection of breast cancer.

The new regulations, which go into effect on September 10, 2024, require mammography facilities to tell women about their breast density. Before this update, notifications were done on a state-by-state basis. 

As of 2022, 38 states and the District of Columbia had laws requiring facilities to notify women about their breast density and increased risk for breast cancer. However, the specific language used in these letters varied from one state to another.

Limitations with breast density notification laws

Breast density notification laws have been controversial. Though experts agree on the importance of increasing awareness about breast density, some have expressed concerns that the information might cause women more anxiety.

Another concern is that women who get one of these letters might not understand its meaning. A 2020 study Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  suggests that women in states with notification laws were more likely to know their breast density status. Still, they didn’t understand how their breast density affected their breast cancer risk. 

2019 study Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  suggests that primary care doctors didn’t recommend additional breast cancer screenings to women with dense breasts even with laws in place.

What do the new regulations change?

The updated regulations aim to make breast density easier for women to understand. The reports imaging centers send to women and their mammogram results will include the language “dense” or “not dense.”

The letters will also recommend that women with dense breasts talk with their doctor about their breast density and cancer risk and ask whether they need additional imaging scans.

Tomosynthesis (3D mammogram), (MRI), and breast ultrasound might help find breast cancers that don’t show up on mammograms. There aren’t any official guidelines on when to use these tests.

However, breast cancer screening is a vital part of women’s health. Talk with your doctor about prevention and regular screening guidelines according to your age and medical history.

Was this helpful?
  1. Berg, W.A. (2021). Screening algorithms in dense breasts: AJR expert panel narrative review.
  2. Breast density and your mammogram report. (2023).
  3. Brown, J. (2019). Physician knowledge, attitudes, and practices regarding breast density.
  4. Dense breasts: Answers to commonly asked questions. (2023).
  5. FDA updates mammography regulations to require reporting of breast density information and enhance facility oversight. (2023).
  6. Hallowell, S. (2023). Breast density notification laws have passed, but now what?
  7. Kyanko, K. A. (2020. Dense breast notification laws, education, and women's awareness and knowledge of breast density: a nationally representative survey.
  8. Mammography quality standards act. (1992).
  9. Sudhir, R. (2020). Diagnostic accuracy of contrast-enhanced digital mammography in breast cancer detection in comparison to tomosynthesis, synthetic 2D mammography and tomosynthesis combined with ultrasound in women with dense breasts.
  10. What does it mean to have dense breasts? (2022).




Medical Reviewer: Elizabeth Berger, MD, MS
Last Review Date: 2023 Mar 31
View All Treating Breast Cancer Early Articles
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