Does Breast Density Affect Mammogram Results?

by Laura Dominici, MD

Mammograms are the most effective tool for screening women for breast cancer. But mammography isn’t perfect: it may be slightly less effective for women with dense breasts.

About half of all women have fairly dense breasts, which contain relatively large amounts of fibrous and glandular tissue and less fat. (Fibrous tissue supports and gives shape to the breast; glandular tissue produces and transports milk.) Breast density, which tends to be high in young women, often declines with age.

Surgical Oncologist Laura Dominici, MD

On a mammogram, dense breast tissue appears as light gray or white, the same shades that can indicate a cancer. On the one hand, this may make tumors harder to detect. On the other, it can result in more false-positives, in which an area that initially appears to show a tumor proves – after further testing – to be non-cancerous.

The letter sent to a woman describing the results of her mammogram doesn’t mention breast density. However, breast density is included in the mammogram report sent to her physician. When an area of concern turns up on a physical exam of a woman with dense breasts, it should be a cue for her physician to explain how density affects mammogram results and how to understand those results. If a woman is concerned that the density of her breasts may reduce the reliability of her mammogram, she should address the issue with her physician.

Despite the potential limitations of mammography for dense breasts, it remains the best, most useful screening technology that we currently have.


Laura Dominici, MD, is a surgical oncologist in the Breast Oncology Center at Dana-Farber/Brigham and Women’s Cancer Center, and an instructor in surgery at Harvard Medical School.