Dense breasts have less fatty tissue and more non-fatty tissue compared to breasts that aren't dense.
Research has shown that dense breasts:
- can be twice as likely to develop cancer as nondense breasts
- can make it harder for mammograms to detect breast cancer; breast cancers (which look white like breast gland tissue) are easier to see on a mammogram when they're surrounded by fatty tissue (which looks dark)
About 43% of women ages 40 to 74 years old in the United States are classified as having dense breasts.
Still, no one method of measuring breast density has been agreed upon by doctors. Breast density is not based on how your breasts feel during your self-exam or your doctor’s physical exam. One way to measure breast density is the thickness of tissue on a mammogram. The BI-RADS (Breast Imaging Reporting and Database System), which reports the findings of mammograms, also includes information on breast density. BI-RADS classifies breasts as one of four groups:
- mostly fatty
- scattered areas of density
- consistently dense
- extremely dense
This way of measuring breast density is based on a radiologist reading the mammogram and deciding if the tissue is dense. Because radiologists are human, there is some subjectivity in breast density classification. If a woman’s breasts are in the middle of the density spectrum, one radiologist may classify them as dense while another may not.
A Norwegian study using automated software to measure breast density has confirmed that women with dense breasts have higher recall and biopsy rates after a mammogram, as well as a higher risk of breast cancer.
The research was published online on June 26, 2018 by the journal Radiology. Read the abstract of “Automated Volumetric Analysis of Mammographic Density in a Screening Setting: Worse Outcomes for Women with Dense Breasts.”
The study included information from 107,949 women ages 50 to 69 who had 307,015 screening mammograms from 2007 to 2015. The researchers used automated software to analyze the mammograms and classify the women’s breasts as dense or not dense:
- 28% of the women were classified as having dense breasts
- 72% of the women were classified as having nondense breasts
The recall rate, which is the rate at which women are called back for more testing based on what looks like a suspicious area on a mammogram, was:
- 3.6% for women with dense breasts
- 2.7% for women with nondense breasts
The biopsy rate, meaning the percentage of women who had biopsies based on a suspicious area on a mammogram, was:
- 1.4% for women with dense breasts
- 1.1% for women with nondense breasts
Rates of cancer detected by mammogram were:
- 6.7 cancers per 1,000 exams for women with dense breasts
- 5.5 cancers per 1,000 exams for women with nondense breasts
Interval breast cancer, which is breast cancer found in between mammograms, usually by self-exam or a doctor’s exam, was:
- 2.8 per 1,000 exams for women with dense breasts
- 1.2 per 1,000 exams for women with nondense breasts
Mammographic sensitivity, or the ability of a mammogram to detect breast cancer, was:
- 71% in women with dense breasts
- 82% for women with nondense breasts
The researchers also noted that cancers detected by mammogram were at a more advanced stage in women with dense breasts compared to women with nondense breasts:
- average tumor size was 16.6 mm in dense breasts compared to 15.1 mm in nondense breasts
- 24% of women with dense breasts had cancer in the lymph nodes compared to 18% of women with nondense breasts
"This study is important for two main reasons," wrote Liane Philpotts, M.D., of the department of radiology at the Yale School of Medicine, in an accompanying editorial. "First, the study provides validation that automated means of density classification can correctly identify a percentage of women with dense tissue. Second, women with dense tissue have poorer performance at screening mammography. This study lends support to the density notification movement, along with redoubling efforts towards optimizing methods of supplemental screening."
As of June 2018, 34 states have passed legislation requiring that women be notified of their breast density with mammography results.
If you know that you have dense breasts, there are lifestyle choices you can make to keep your risk of breast cancer as low as it can be, including:
- maintaining a healthy weight
- exercising every day
- limiting or avoiding alcohol
- eating a healthy diet full of fresh, whole foods and avoiding processed foods with a lot of added sugar and salt
- never smoking (or quitting if you do smoke)
- breastfeeding, if you have the option to do so
Along with lifestyle options, many doctors recommend additional screening for women with dense breasts. This might include MRI and ultrasound.
For more information on steps you can take to keep your breast cancer risk as low as it can be if you have dense breasts, visit the Dense Breasts page in the Breastcancer.org Lower Your Risk section.
To talk with others who have an increased risk of breast cancer, join the Breastcancer.org Discussion Board forum High Risk for Breast Cancer.