Dense breasts have less fatty tissue and more non-fatty tissue compared to breasts that aren't dense.
One way to measure breast density is the thickness of tissue on a mammogram. 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
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. Dense breasts have more gland tissue that makes and drains milk and supportive tissue (also called stroma) that surrounds the gland. Breast density can be inherited, so if your mother has dense breasts, it's likely you will, too.
Research has shown that dense breasts:
- can be 6 times more likely to develop cancer
- 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.
As of Jan.1, 2016, 24 states have passed legislation requiring that women be notified of their breast density with mammography results.
A study has found that most notification letters about breast density use very technical language and can be hard to understand.
The research was published in the April 26, 2016 issue of JAMA. Read the abstract of “Content, Readability, and Understandability of Dense Breast Notifications by State.”
To do the study, the researchers reviewed the breast density notification letters from 23 of the 24 states (Delaware’s notifications were not included):
- 21 states require that specific language be used in the letters
- 4 states only require that specific topics be included
- 7 states require a generic notification letter be sent to every woman who gets a screening mammogram
- 16 states require that only women with dense breasts receive a notification letter
- all the notification letters mentioned that dense breasts can mask cancer on a mammogram, called “masking bias” by doctors
- 18 letters mentioned that dense breasts have a higher risk of cancer
- 14 letters mentioned the option of additional breast cancer screening and advised women to talk to their doctors
- 6 letters mentioned that women with dense breasts might benefit from additional screening
- 4 letters mentioned specific types of additional screening, such as MRI or ultrasound
The researchers also measured the readability of the letters with the Flesch-Kincaid test in Microsoft Word. The Flesch-Kincaid test analyzes the words used in a document and then offers a score as a U.S. school grade level, though there is no top level. Anything over grade 12 is considered very hard to understand.
About 20% of the U.S. population reads below a fifth grade level. In general, experts recommend writing at grade 7 or 8 to make sure that most people understand the content.
The readability of the letters ranged from grade 7 to grade 19.4. Most of the letters had scores higher than grades 7 or 8. States with the lowest literacy levels had letters with some of the highest readability scores.
The authors said that if a woman has a hard time understanding the letter she receives about her breast density, she may have trouble making decisions about whether to have additional screening because she’s not sure if it will offer benefits for her.
While the results of this study are troubling, there is something you can do. If you receive a letter that talks about your breast density and you don’t understand it, call your doctor’s office and ask someone there to help you interpret the letter. Together, you and your doctor can decide if more screening with a different test would benefit your unique situation.
For more information on dense breasts and the additional screening tests that are used, visit the Having Dense Breasts page in the Breastcancer.org Lower Your Risk section.