What You Need to Know About Dense Breasts and Mammograms

Having dense breast tissue is normal and fairly common. However it generally makes it harder for doctors to detect cancer on mammograms.

Mammograms (x-ray pictures of the breast), which help doctors detect tumors that cannot be felt, are an essential breast cancer-screening tool for women. Doctors also use mammograms as a diagnostic tool to take detailed pictures of suspicious areas revealed by a screening mammogram.

Although mammograms can be very useful in spotting tumors, there are some pitfalls. Mammograms may not spot all breast cancers, especially when women have dense breast tissue.

One of the downsides of mammogram technology is the risk of false-negative results. That’s when a mammogram appears to be normal in spite of breast cancer being present. According to a recent National Cancer Institute (NCI) Fact Sheet: “Overall screening mammograms miss about 20 percent of breast cancers that are present at the time of screening.” One major reason for false negative results from mammography is increased breast density.

NCI notes: “Breast density describes the relative amount of different tissues present in the breast. A dense breast has less fat than glandular and connective tissue.”

Breast density cannot be determined accurately by a physical examination. “Currently, the determination of density by radiologists is a qualitative, visual assessment requiring a mammogram,” says Mark D. Kettler, MD, associate professor of diagnostic radiology; Oregon Health & Science University, Section of Women’s Imaging. He adds, “Evolving technologies may provide more objective and quantitative density assessment in the future.”

(Copy, breast images and pie chart above courtesy of American College of Radiology, www.acr.org)

Dr. Kettler says that generally, though not always, younger women have denser breasts and as women age, the ratio of fatty tissue to dense issue (fibroglandular tissue, which is both glandular and connective tissue) increases. “Generally, the fattier the breast tissue, the easier it is to spot abnormalities including masses, calcifications and distortions of tissue,” explains Kettler. According to the NCI, “Mammogram films of breasts with higher density are harder to read and interpret than those of less dense breasts.”

“Our recommendation is to get a baseline mammogram at age 40 to determine breast density and go from there based on risk,” explains Kettler. “If women are committing to yearly screening beginning at age 40 based on dense breast tissue, there is a role for digital tomosynthesis in lieu of conventional mammography.”