What’s the deal with breast density?
Dear Breast Friend, My radiologist said I was dense. I said ‘Rude, but okay.’ Apparently she was talking about my mammogram- what does this even mean? Sincerely, Dense as my mother-in-law’s pound cake
Dear Dense,
Don’t take offense, you are in good company! Almost 50% of women have dense breast tissue.
A normal finding. The first thing to know about breast density is that, whatever your density is, it is normal for you. Breasts are made up of different types of tissue:
Glandular tissue which is made up of lobules that produce milk and ducts that transport milk
Fibrous or connective tissue that supports and holds the breast in place
Fatty tissue which helps give breasts their size and shape and fills the space between fibrous and glandular tissue
Both glandular tissue and fibrous tissue show up as ‘white’ on the mammogram, and are often discussed together as “fibroglandular” tissue. Fatty breast tissue appears ‘black’ on the mammogram. Breast density is a measure of how much white fibroglandular tissue there is in the breast relative to black fatty tissue. If you have higher breast density, it means that your breasts are comprised of more fibroglandular tissue compared to fat. The pattern of how the different types of glandular tissue are distributed in a breast is completely unique to each person. In that way, a mammogram is similar to a fingerprint- no two mammograms look the same! It is important to note that breast density is solely determined by the appearance of the tissue on imaging, not what the tissue feels like on clinical exam.
Why density is important. There are two very important reasons your radiologist cares about breast density. First, dense breast tissue can mask or hide breast cancer. Since breast cancers often show up as ‘white’ on the mammogram, when you are looking for breast cancers on a mammogram with a lot of dense tissue it can be a little like looking for an arctic fox or polar bear in a blizzard! Very difficult. Second, dense breast tissue is an independent risk factor for breast cancer which means the denser your tissue, the higher your breast cancer risk! Click here to learn more about breast cancer risk assessment.
Dense breast causes. Dense breasts are normal and occur in nearly half of women over the age of 40. On average, breast density is higher in women under the age of 40 and tends to decrease as women get older, but some women will remain dense throughout their lifetime or can become dense as they get older. Asian women are more likely to have dense breasts than women of other races. Studies investigating whether Black or Hispanic women have denser breasts than their white counterparts have yielded mixed results. Other factors that can increase breast density include pregnancy and breastfeeding, hormone replacement therapy, and have a lower body weight.
Levels of density are described using the American College of Radiology's Breast Imaging Reporting and Data System, which is sometimes shortened to BI-RADS. The levels of density will sometimess be included in a mammogram report using letters A-D. The levels of density are:
A: Almost entirely fatty This means that the breasts are almost entirely made up of fatty tissue. There is very little dense breast tissue.
B: Scattered areas of fibroglandular density This means the breasts are mostly made up of fatty tissue, but there are some scattered areas of dense breast tissue.
C: Heterogeneously dense This means that most of the breast tissue is dense breast tissue, but there are some areas of fatty tissue.
D: Extremely dense This means that nearly all of the breast tissue is dense breast tissue. There is very little fatty tissue.
In general, you are considered to have dense breasts if your mammogram report says you have heterogeneously dense or extremely dense breast tissue.
Mammograms are still important. Even though it is more difficult to find breast cancers on mammograms in the setting of dense breast tissue, it is still vitally important to continue with recommended yearly screening mammograms. There are certain early signs of breast cancer, like calcifications and distortions, that are best demonstrated on a mammogram. Women with an average risk of breast cancer are recommended to begin screening with mammograms at age 40. Women at high risk of breast cancer are recommended to start screening mammograms at age 30. Mammograms are proven to reduce the risk of dying of breast cancer and remain a central part of breast cancer screening programs.
A better mammogram. Newer mammogram technologies help improve the chances that cancer will be detected. For instance we now use digital pictures instead of film pictures. Digital pictures let the radiologist zoom in to take a close look at anything concerning. Additionally, a 3D or tomosynthesis mammogram uses computers to combine multiple X-ray pictures of the breast into a 3D image. This helps smooth out overlapping dense tissue and makes it easier to see real findings. At GRACE, we use both digital and tomosynthesis technology as our standard of care to give our patients the most accurate results.
Supplemental imaging. Other types of tests look at breast tissue a different way than a mammogram and can help find additional cancers in the setting of dense breast tissue. However, there is a trade off; tests such as ultrasound and MRI may find things that result in additional testing but are later found to not be cancer. This is called a false-positive result. While all of the supplemental breast exams can find more breast cancers than a mammogram alone, more research is needed. There are benefits and drawbacks to each type of testing, so it is important to discuss the options with your healthcare team. Additional tests that might be used in those with dense breasts include:
Breast MRI. Breast MRI uses a magnetic field and radio waves to make 3D images of the breast tissue. It's often recommended for those with a very high risk of breast cancer or dense breast tissue.
Breast ultrasound. Ultrasound uses sound waves to make images of tissues in the body. It shows the difference between fluid-filled sacs called cysts and solid masses. Solid masses may be a sign of cancer. A diagnostic breast ultrasound is commonly used to take a closer look at areas of concern detected on a mammogram.
Contrast-enhanced digital mammogram. A contrast-enhanced digital mammogram uses liquid contrast dye that contains iodine. The contrast material can highlight possible areas of concern on a mammogram. The contrast material goes into a vein in your arm though an IV. After waiting a few minutes for the contrast to reach the breast tissue mammogram pictures are taken.
At GRACE, we are here to be a resource for you if you have any questions about your breast density. We can support you as you decide which tests are best for you based on your personal risk factors for breast cancer.