Dense Breasts

Approximately 40-50% of women over the age of 40 are considered to have dense breasts. The breast is normally composed of fat and glandular tissue – the higher the proportion of glandular tissue, the denser the breast. Dense breast tissue appears “white” on a mammogram, and the challenge is that cancers also will often appear as a white mass on mammogram. “Lumpy” breast tissue is not the same as dense breast tissue – density is determined by the appearance on a mammogram, not by feel.Approximately 10-20% of breast cancers are missed by standard mammography, and that percentage can approach 40-50% in women with dense breasts. In addition, women with dense breasts have an increased risk of developing breast are many factors that influence breast density including age, hormone levels, genetics, age at first pregnancy, number of pregnancies, use of hormone replacement therapy, and overall body weight – just to name a few. Younger women naturally have denser breast tissue, but that does not mean that all young women are at increased risk for breast cancer. The risk of breast cancer increases with age, and it is hard to sort out when the increased risk develops in relation to breast density.Over the past several years, there has been an increased awareness of the significance of dense breasts. Mammogram reports contain a notation of breast density, but the “layperson letter” that the patient receives does not always contain this information.

Several states (including California) have passed legislation requiring that patients be informed of their breast density. Federal legislation is pending regarding this matter. If you have dense breasts, and your mammogram is performed in California, your lay letter will contain this wording:

  • Your mammogram shows that your breast tissue is dense. Dense breast tissue is common and is not abnormal. However, dense breast tissue can make it harder to evaluate the results of your mammogram and may also be associated with an increased risk of breast cancer.
  • This information about the results of your mammogram is given to you to raise your awareness and to inform your conversations with your doctor. Together, you can decide which screening options are right for you. A report of your results was sent to your physician.

Tomosynthesis, also known as 3D mammography, can improve the rate of breast cancer detection in women with dense breasts, but as there are no long-term studies to show if outcomes are improved, and, insurance may not cover this form of imaging. Tomosynthesis may be associated with slightly higher radiation exposure compared to 2D digital mammography. While we may be able to detect smaller lesions with these newer techniques, concern has been raised about the issue of overdiagnosis and overtreatment – finding lesions that will never be of any significance to the patient.

We know that breast MRI and ultrasound, including automated whole breast ultrasound, can be very helpful in evaluating women with very dense breast tissue. These additional tests may not be covered by insurance. However, there is no perfect imaging technique for dense breasts – all of the available modalities have the potential to miss cancer. My recommendation is that women speak to their doctors and ask questions. Ask if your breast tissue is dense, and if so, request that the benefits and possible risks of additional testing be reviewed.

Dr. Attai was one of the physicians invited to testify before the California Legislature in support of SB 1538, which was eventually signed by Governor Brown, requiring that imaging facilities in California inform women if they have dense breasts on mammography.

Updated 15 June 2019