Your breast density is critical when it comes to understanding your breast cancer risk. Breast density is a measurement of the amount of fibroglandular, or connective, tissue. The more fibroglandular tissue you have, the denser your breasts. When a radiologist reads your mammogram, she defines your breast density as being one of four categories. Those categories are:
Predominantly fatty (only 0-25% fibroglandular tissue)
Scattered fibroglandular (25-50% fibroglandular tissue)
Heterogeneously dense (50-75% fibroglandular tissue)
Extremely dense (greater than 75% fibroglandular tissue)
This characterization is important because it helps radiologists determine whether a patient requires additional evaluation. Up to 50 percent of US women have dense breast tissue. Younger, pre-menopausal women tend to have denser breast tissue. Why does this matter?
Dense breast tissue makes it harder to see small, early breast cancers. This is because fibroglandular tissue and breast cancer can look similar on a mammogram. In addition, women with heterogeneously dense or extremely dense breasts have a higher risk of developing breast cancer than women with predominantly fatty or scattered fibroglandular breast tissue. Women who are at intermediate risk or high risk, based on their breast density, should use breast ultrasound as an additional tool in screening for breast cancer, as up to 35 percent of breast cancers are not seen by mammograms in women with dense breasts. However, it is still critical for all women over age 40 to get annual mammograms.
Automated breast ultrasound is quick, painless, and accurate. The test takes hundreds of images of the entire breast. These images are reconstructed into a 3D image that can be read by radiologists. This provides a picture of the entire breast, rather than a smaller area. Having a 3D image set allows radiologists to look at the images from many different angles to accurately diagnose any abnormality. If additional imaging is needed, the radiologist will report that the exam is incomplete and ask the patient to have additional handheld ultrasound imaging of the area in question. The handheld ultrasound images can help radiologists determine whether the suspicious area is benign (usually a cyst) or whether it needs further evaluation through a biopsy. Keep in mind that most biopsy results are benign as well, so a biopsy does not mean that there is a breast cancer.
To ensure that you are getting the best possible care, ask your doctor whether you have dense breast tissue. If you do, request a screening breast ultrasound in addition to your annual mammogram, as this exam can help detect small breast cancers that would not otherwise be seen on mammogram. In short, a screening breast ultrasound could save your life by showing a small, curable cancer rather than waiting until it is larger and less curable.
 Screening breast ultrasound can also be referred to as automated breast ultrasound (ABUS), whole breast ultrasound, or 3D breast ultrasound.