New Mammography Study Examines Association Between Breast Density Changes and Breast Cancer Risk

Increases in breast density over three consecutive biennial mammography screenings led to significantly elevated breast cancer risks for pre- and postmenopausal women, according to a new longitudinal retrospective study of over 2.2 million Korean women who had no prior history of breast cancer.

Drawing from a Korean National Health Insurance Service database, the study authors retrospectively reviewed data from 2,253,963 women, including 1,356,846 women with fatty breasts at baseline and 897,117 women who had dense breasts at the baseline of the study.

In the recently published study in Radiology, the researchers noted that premenopausal women with fatty breasts at the first mammography exam and a subsequent fatty to dense presentation for the second and third exams had a 1.45 hazard ratio for breast cancer in comparison to women who maintained fatty breasts throughout the three biennial screenings. Those with an initially fatty to dense to fatty progression had a 1.53 hazard ratio and those with initially fatty to dense-to-dense breast progression had a 1.93 hazard ratio according to the study.

In comparison to postmenopausal women with stable breast density, postmenopausal women with fatty breasts at baseline and a subsequent dense-to-dense progression had a 1.62 hazard ratio for breast cancer, according to the study.

For premenopausal women with dense breasts at baseline, the researchers noted that those with a subsequent fatty-to-fatty breast progression had a greater than 20 percent reduction in breast cancer risk (hazard ratio of 0.62) in comparison to those with a fatty-to-dense progression (hazard ratio of 0.85) or a dense-to-fatty progression (hazard ratio of 0.84).

“Cumulative evidence from this study and those of previous studies suggest that shifting the distribution of dense breasts to fatty or scattered fibroglandular breast density would considerably reduce breast cancer risk,” wrote study co-author Boyoung Park, M.D., Ph.D., who is affiliated with the Department of Preventive Medicine at the Hanyang University College of Medicine in Seoul, Republic of Korea, and colleagues. “Reductions in breast density among women with dense breasts could be achieved through increased breastfeeding and primary prevention with tamoxifen citrate for women at the highest risk.”

In an accompanying editorial, Masako Kataoka, M.D., Ph.D. praised the subgroup analysis from the large study cohort and the inclusion of covariates of breast cancer risk that facilitated appropriate adjustments to hazard ratios.

“These epidemiologic analyses, which are often missing in imaging-based papers, are important to demonstrate the density-related factors are independent risk factors,” noted Dr. Kataoka, the chief of breast imaging and a lecturer in diagnostic imaging and nuclear medicine at Kyoto University Graduate School of Medicine in Kyoto, Japan.

“Reductions in breast density among women with dense breasts would avert 28.9% of breast cancers among premenopausal women and 14.4% among postmenopausal women, which would prevent more events than reducing any other risk factor in this study,” emphasized Park and colleagues.

In regard to study limitations, the authors noted the study cohort did not include women under the age of 40, which prohibited assessment of breast cancer risk in younger women with dense breasts. They also pointed out that information about genetic or molecular factors was not available. Employing the four categories of BI-RADS to assess breast density, Park and colleagues said they did not distinguish whether benign lesions were included in breast density assessments. The study authors also acknowledged a mixture of single and double reads of mammograms from the study database.