Racial differences in breast density may affect cancer risk assessment, screening

A quantitative analysis showed black women had greater breast density than white women, and this finding could have implications for breast cancer risk assessment and screening, according to researchers.

Increased breast density is a strong risk factor for breast cancer, partly because it decreases sensitivity of mammographic screening.

“Racial differences in breast density would have implications for breast cancer risk assessment and could lead to different screening practices for women in many states,” Anne Marie McCarthy, PhD, of the department of general internal medicine at Massachusetts General Hospital, and colleagues wrote.

Black women tend to have higher breast cancer mortality, are diagnosed with later-stage disease, and have higher incidence of poor-prognosis and triple-negative breast cancers than white women. However, studies designed to assess racial differences in breast density have yielded conflicting results.

McCarthy and colleagues reviewed electronic medical records for 9,490 women who underwent routine digital mammography screening at Hospital of the University of Pennsylvania between Sept. 1, 2012, and Aug. 31, 2013.

Researchers compared breast density of 5,282 black women (median age, 57 years) with 4,216 white women (median age, 57.3 years). Validated, automated software provided estimated measures for dense area, area percent density, dense volume and volume percent density.

Black women had a higher mean BMI than white women (32.4 vs. 26.4).

Researchers reported similar levels of dense area between black women and white women. However, black women had lower area percent density (12.3% vs. 17.1%, P < .001), greater volume of dense tissues (266.9 cm³ vs. 196.1 cm³; P < .001) and lower volume percent density (9.8% vs. 11.6%; P < .001).

The researchers observed a statistically significant interaction between race and BMI for all quantitative density measures (P < .001).

After accounting for age, BMI and breast cancer risk factors, no racial differences existed in the likelihood for high density as determined by the Breast Imaging Reporting and Data System (BI-RADS) density for nonobese or obese women.

However, black women had greater odds for high breast density in all quantitative measures. Their risks were 40% to 51% higher for dense area, 18% to 26% higher for area percent density, 27% to 55% higher for dense volume, and 32% to 65% higher for volume percent density.

The researchers acknowledged the study was limited by the fact BMI was obtained from medical records at the time of mammography or shortly before, allowing for the possibility that results were based on both self-reported and measured BMI.

“These data emphasize the need to further investigate breast density measurements and their relationship to both screening and cancer outcomes if breast density will be used in large-scale policy interventions for breast cancer prevention and early detection,” McCarthy and colleagues wrote.

It also may be important to examine the independent contributions of dense breast volume and BI-RADS breast density in relation to rates of interval cancer and absolute risk for breast cancer, Karla Kerlikowske, MD, of the San Francisco Veterans Affairs Medical Center, and Celine M. Vachon, PhD, of the division of epidemiology at Mayo Clinic in Rochester, Minnesota, wrote in an accompanying editorial.

“Breast cancer risk prediction models that incorporate BI-RADS breast density are being

used to identify women with dense breasts at high risk [for] interval cancer, tailor screening — including starting and stopping ages and screening interval — and identify those eligible for primary prevention,” Kerlikowske and Vachon wrote. “Thus, the different nature of breast density measurements, whether estimated subjectively by radiologists or automated by programs, likely provide complementary information to inform breast cancer risk.” – by Kristie L. Kahl

Disclosure : The study was funded by the NCI.