Breast Density – What does it mean?!?

Mammogram reports now frequently include a notation of breast density and a disclaimer that this may reduce the ability of the mammogram to detect cancer.  Naturally this is a bit alarming

First of all, it is important to realize that dense breast tissue is not abnormal.  Almost half of women have dense breast tissue and women with dense breasts do NOT have an increased risk of dying from breast cancer. The term itself is a term that describes how your mammogram image looks, not how the breast tissue feels on exam.  It is the relative amount of black (fat tissue) on the image to white (glandular tissue) on the image.

Increased density is more common in women who are younger, on hormones, have a higher weight,  with history of previous pregnancies and those who have used tamoxifen or have family history of dense breasts. There is also subjective differences in assigning breast density, meaning different radiologists may interpret the image differently.

The scale that defines the breast density is called Bi-Rads and categorizes women into 4 groups:

  • A – Almost entirely fatty
  • B – Scattered areas of fibroglandular density
  • C – Heterogeneously dense (may obscure small masses)
  • D – Extremely dense (lowers the sensitivity of mammography)

For most purposes, the term “dense breasts” refers to either heterogeneously dense or extremely dense breasts (categories C or D).

Denser breasts have a few implications.  First, it may obscure the detection of a mass in the breast.  Second, it does slightly increase the risk of developing breast cancer. For these reasons it is important not to ignore the classification, but it is equally important not to over inflate the significance of it.

While studies have shown that breast ultrasound and MRI can help find some breast cancers that can’t be seen on mammograms, they can also show more findings that are not cancer. This can lead to more tests and unnecessary biopsies. Additionally, the cost of an ultrasound or MRI may not be covered by insurance.   So really the trick is figuring out who needs additional imaging because they have increased breast cancer risk and who “just has normal dense breasts”.

There are several online tools that can help estimate your risk of breast cancer such as  In general, these models do not take breast density into account, but can still guide the decision how to follow up after a mammogram with this finding.

  • A woman with <15% risk of breast cancer, then no additional screening is recommended regardless of breast density.
  • A risk of 15-20% is a gray zone, with most organizations recommending a shared decision with your provider. Additional imaging with MRI or ultrasound may be an option, but neither modality is routinely covered by insurance for this risk category in most states.
  • With a risk >20% most groups recommend supplemental testing. Frequently women with higher cancer risks will be referred to a specialty breast care center to determine the best management options.

Regardless of risk, there are lifestyle factors which can decrease your chances of developing breast cancer.  Exercise and limiting weight gain, especially in the postmenopausal years, a low-fat diet, limiting alcohol intake and not smoking have all been shown a lower breast cancer rate. Screening modalities can be different as well.  Digital tomosynthesis, or 3D mammography, may be more sensitive for women with dense breasts and pick up more cancers than traditional 2D mammograms.  Most women who have had 3D imaging do not need further imaging because of dense breasts.