A woman's breast density changes over her lifetime, decreasing with age and correlating with her menopausal status. Breast health specialists are focusing on how much breast density augurs a risk for breast cancer. Two recent studies offered some insights into the link between mammographic density and disease risk.
Researchers at the Mayo Clinic suggested that a reduction in breast density over time conferred a lower breast cancer risk, while investigators at Georgetown University hypothesized that increases in breast density may be associated with estrogen and progestin therapy.
CELINE VACHON, PHD
Celine Vachon, PhD, and colleagues tapped into the Mayo Mammography Health Study of nearly 20,000 women. "Breast density is not a static trait," said Dr. Vachon, an associate professor of epidemiology at the Mayo Clinic in Rochester, Minn. "We know that it changes. We have seen that it decreases with increasing age and with postmenopausal status."
The women included in this analysis underwent a screening mammogram between October 2003 and September 2006. Women were eligible if they were 35 years of age or older, had no personal history of breast cancer, and lived in Minnesota, Iowa, or Wisconsin (all three states have breast cancer registries).
"We were able to access mammograms as early as 1996 for the women in the study to assess change in density," Dr. Vachon said. "Change in density was measured over an average of six years between the earliest and the enrollment mammograms." Women were followed for an average of four years for breast cancer. Breast density categories, as determined by the Breast Imaging Reporting and Data System (BI-RADS), are: primarily fatty breast tissue, scattered densities, heterogeneously dense, and extremely dense.
Dr. Vachon reported on 219 women with new breast cancers and compared their outcomes with 1,900 women selected randomly from the mammography cohort. Dr. Vachon noted a reduced risk in those women who had decreased one BI-RADS category or more over an average six years (hazard ratio = 0.72). These women were at reduced risk of breast cancer compared with those whose density was unchanged (AACR 2010 abstract 4828).
The researchers also observed an increased risk of 52% for women whose breast density increased by one BI-RADS category or more, but it did not achieve statistical significance (HR = 1.52), she said.
When the researchers looked at women's menopausal status, "the decreased risk associated with decreased density appears to be significant only among postmenopausal women," Dr. Vachon said. But she noted that the figures were derived using 62 cases among premenopausal women and 157 cases among postmenopausal women. "So it could be that we were not powered to detect an association in the premenopausal group," she said.
Her group suggested that measures of breast density at two time points may inform women's risk beyond a measure at one point in time.