Your Guide to Understanding Breast Density

A: Breast density is a measure of how much fibroglandular (dense) tissue is present in a woman’s breast compared to how much fatty tissue is present. Breast density can vary with factors such as age, changes in weight, and hormone usage, but for many women it does not change throughout adulthood.

A: The doctor who reads your mammogram will indicate in their report which of the 4 density categories best matches the appearance of your breasts. This information will be sent to your doctor and you will also be notified in your results letter.

A: Breast density does not relate to how breasts look or how firm they feel. The only way to determine how much dense tissue is present is with an imaging test like a mammogram.

A: Breast density is important for two reasons. First, dense breast tissue can hide a cancer on mammography. Dense tissue looks white on a mammogram. Cancers also look white on a mammogram, so they may not stand out against the background of dense tissue. Fatty tissue looks dark gray on a mammogram, making cancers much easier to spot. Second, recent research has shown that having dense breasts may also be a risk for getting breast cancer, independent of family history or other risk factors. Though this risk is small, it is significant. For women with heterogeneously dense tissue, the risk is about 1.2 times that of the average woman. For women with extremely dense tissue, the risk is about 2 times that of the average woman. For comparison, the risk for a woman who had no children before age 30 is 1.9 times that of a woman who had children earlier.

A: Yes. Mammography is the only test of any kind proven to save lives from breast cancer. Some of the earliest breast cancers are only visible on mammography, even in patients with dense breasts. Yearly mammography is recommended for all women over the age of 40. Any other tests should be performed in addition to mammography, not instead of mammography.

Breast Tomosynthesis (also known as 3D mammography) has been shown to find additional cancers in women with all types of breast density and has also been shown to reduce the number of women recalled for additional imaging. All women should consider tomosynthesis to maximize the benefits of mammography.

A: Regardless of your breast density, it can be helpful to speak with your healthcare provider about your individual risk for breast cancer. MRI has been recommended for many years as a supplement to mammography for all women with a 20% or greater lifetime risk of breast cancer. This includes women with genetic mutations such as BRCA and their close relatives, women with a history of radiation therapy to the chest between the ages of 10 and 30 (such as those who had Hodgkin’s Disease), and other high risk patients. The American College of Radiology recently updated its guidelines to also recommend yearly MRI for women with a personal history of breast cancer plus dense breasts and women with any breast density who had breast cancer before age 50. MRI is often covered by insurance for women with these types of risk factors.

If your breasts are dense, but you do not have other risk factors, you and your provider should discuss additional screening options, which can find some additional cancers, but can also lead to further testing and biopsies for findings that are not cancerous.

If you choose to have additional screening, MRI is the test that has been shown to find the most additional cancers while minimizing the number of additional tests needed for findings that are not cancer. The most important large national study that compared mammography, MRI, and ultrasound showed that the most cancers were found with the combination of mammography and MRI. Adding ultrasound to this combination did not find any additional cancers and resulted in recommendations for many more biopsies – more than 92% of which did not show cancer. For these reasons screening breast ultrasound should only be considered for patients who medically cannot have MRI.

Recently, a new type of MRI called “Fast MRI” has been developed to provide a quicker, less-costly alternative for women with dense breasts who do not have additional risk factors.