Why Are Dense Breasts a Breast Cancer Risk?

Doctor and patient using digital tablet in clinic
Hero Images/Getty Images

Breast density is one of the risk factors for breast cancer. Yet, until a woman has a first mammogram she doesn’t know if she has dense breasts. Breast density can only be determined by a radiologist when reviewing a mammogram. It can’t be felt. Dense breasts don’t mean firm breasts.

The four categories of breast density begin with breasts that are the least dense, having almost all fatty tissue, to the last category, which describes the most dense breasts as being almost all glandular and fibrous with little to no fatty tissue.

Having dense breasts carries a risk because:

  1. Although the reasons are unknown at this time, it is known that having dense breast tissue increases a woman’s risk for breast cancer. According to the American Cancer Society, it does not mean that a woman who has dense breasts has a high risk overall. There are many risk factors for breast cancer. A woman’s overall risk depends on all risk factors taken together.
  2. Dense breast tissue can make it difficult to see a cancer on a mammogram since dense breast tissue appears white, and breast tumors look white.

Over half of women getting mammograms have dense breasts. Mammograms are not recommended for women under 40 years old unless they are in a high-risk group, such as having a gene mutation or an extensive family history of the disease.

While dense breasts can make spotting a cancer more difficult on a mammogram, mammograms are still the screening tool of choice for women with dense breasts.

Digital mammograms are recognized as a more effective screening tool than film mammogram for women with dense breasts. 

Currently, there is no consensus among experts as to what tests need be done beyond mammograms in women with dense breasts. The problem with additional testing, such as ultrasound and MRI, is that they can show findings that are not cancer.

This can result in additional testing and unnecessary biopsies.

High breast density notification laws are in effect in 21 states. It is anticipated that these laws will continue to be enacted in other states. Prior to this legislation, a woman might be called in to see the radiologist following a mammogram and told she has dense breasts. She would be advised to speak with her physician about how to manage monitoring her breast health in the future.

In states where written notifications are the law; women receive a more comprehensive notification, such as:

“Your mammogram shows that your breast tissue is dense. Dense breast tissue is very common and is not abnormal. However, dense breast tissue can make it harder to find cancer on a mammogram and may also be associated with an increased risk of breast cancer.

Use this information to talk with your doctor about your risks for breast cancer. At that time, ask your doctor if more screening tests might be useful, based on your risk. A report on your results was sent to your physician.

If a woman has been told she has dense breasts, the best course of action is to meet with her physician and discuss her medical history, and other factors that might increase her overall risk for breast cancer.


Breast Density and Your Mammogram Report. American Cancer Society. 2016.


Continue Reading