Zeroing in on density and breast cancer risk

WASHINGTON, D.C. – Cancer Digest – Breast density and cancer risk have been the topic of intense research efforts in recent years. At this week's 101st meeting of the American Association of Cancer Research (AACR) scientists presented a trio of studies aimed at quantifying the risk of cancer linked to breast density and, just as importantly, finding a safer way to measure breast  density.


Breast density describes the relative amount of different tissues that compose the breast. A dense breast has more glandular and connective tissue relative to fat. Mammogram images of breasts with higher density have large opaque areas that show as white on the film, obscuring details of the tissue. As a result mammograms of dense breasts are harder to read and interpret than those of less dense breasts. Women whose ratio of dense breast tissues exceed 75 percent on a mammogram have a risk of breast cancer that is four to five times greater than that of women with little or no density, making mammographic breast density one of the strongest biomarkers of breast cancer risk.

In two of the studies presented this week researchers found that changes in breast density over time affected cancer risk. In a study by Dr. Celine M. Vachon, Ph.D., associate professor of epidemiology in the College of Medicine at the Mayo Clinic, showed that women who had a decrease of at least one density category over a six-year period had a 28 percent reduced the risk of developing breast cancer compared with women whose breast density remained stable over that time.

In the second study researchers led by Dr. Celia Byrne, assistant professor of oncology at the Lombardi Comprehensive Cancer Center at Georgetown University, looked at the effect of hormone therapy (estrogen and progestin) on breast density in postmenopausal women who participated in the Women's Health Initiative.

They found that 57 percent of the women in the group that didn't take hormones had a decline in density as shown on mammograms compared with 16 percent of the women in the hormone therapy group. Similarly 47 percent of the placebo group had a modest increase in breast density compared with 85 percent in the hormone group. Significantly, they found that increased risk in cancer among the women with increased breast density closely mirrored the 24 percent increased risk of breast cancer the Women's Health Initiative found for postmenopausal women taking hormones.

One of the obstacles to using breast density to assess and monitor cancer risk, however, is the increased risk posed by repeated mammograms. In the third study, researchers sought to develop a safer method for measuring density. Led by Dr. Gertraud Maskarinec, professor of epidemiology at the Cancer Research Center at the University of Hawaii, the researchers used dual energy X-ray absorptiometry (DXA), which is a low-radiation option to evaluate breast density for younger women who do not undergo mammography. DXA is widely used to evaluate bone density and total body composition.

In the study, the researchers compared breast density measured by DXA with mammographic density among 101 women aged 30 years and older with a normal mammogram. They found the DXA results closely matched mammogram results. Whether DXA is safe enough or accurate enough to be used to determine the cancer risk of breast density, however, remains to be seen.