Race and Breast Density: Understanding the Risk

Black/African-American women had a significantly higher absolute area breast density of 40.1 cm² compared with 33.1 cm² in white women. This research was presented at the 2015 AACR Annual Meeting.

The study enrolled 1,589 black women and 1,256 white women who underwent screening mammography at the University of Pennsylvania from 2010 to 2011. Researchers analyzed all available raw digital mammograms for women who had BMI recorded in electronic medical records at the time of screening.

Data also showed that black women had a significantly higher volumetric density of 187.2 cm³ compared with 181.6 cm³ in white women.

“Since breast density is associated with breast cancer risk, a better understanding of racial differences in breast density levels could help us identify women at the highest risk for breast cancer and target prevention strategies to those women,” Anne Marie McCarthy, PhD, a research fellow at Massachusetts General Hospital and lead author of the study, said in a statement.

Breast density refers to the amount of fibroglandular tissue in the breast when observed on a mammogram. Since the fibroglandular tissue appears as white on the mammogram, it makes it difficult to visually detect breast cancers.

Research has shown that women who have the highest breast density have a four to six times greater risk for breast cancer compared with women with lower breast density.

Although several studies have shown that black women have lower breast density than white women on average, the authors of this study suggest the reason behind that may be partly due to racial differences in BMI, which is inversely associated with density.

Usually, radiologists examine mammograms and assign patients a breast density level, but that assignment can be subjective, McCarthy explained. In this study, which was funded by the National Institutes of Health, researchers used fully-automated computer algorithms to produce both the conventional two-dimensional breast density measurement and a three-dimensional volumetric estimate of breast density. Volumetric estimates of absolute and percent dense tissue were obtained using FDA-cleared tissue.

“Our findings are using a new, quantitative and, perhaps, more reliable way to measure breast density,” McCarthy says.

The mean age of the patients was 57. Results showed that black women had higher mean BMI than white women (32.0 kg/m² vs 26.0 kg/m², P <.001), higher absolute area (40.1 vs 33.1 cm², P <.001), and volume density (187.2 vs 181.6 cm³, P <.001) than white women but lower area (19.6% vs 23.5%, P <.001) and volume percent density (11.6% vs 13.4%, P <.001).

When adjusting for age, BMI, and breast cancer risk factors, black women had higher breast density across all measures (absolute area density β = 0.211, P <.001, area percent density β = .0999, P = .021, absolute volume density β = 0.242, P <.001, volume percent density β=0.221, P <.001).

The results also showed that the interaction between race and BMI was significant for area percent (P = .001) and volume percent density (P <.001) and was near significant for volume density (P = .085); however, for all three measures, BMI was more strongly associated with density among white women than black women.

The researchers concluded that the significantly higher breast density in black women was not explained by BMI or recognized breast cancer risk. Therefore, racial differences in breast density may have implications for disease risk and prevention strategies.

Follow-up ultrasound screening for women with dense breasts continues to garner interest among advocates and researchers, with 22 states enacting breast density reporting laws and legislation pending in Congress. A study presented at the 2014 San Antonio Breast Cancer Symposium drawing on data from radiology practices in Connecticut (the first state to enact legislation mandating breast density reporting) showed that during four years of ultrasound screening of mammographically normal but dense breasts, the follow-up screening did detect a significant number of breast cancers not discovered by mammogram.²

“Our next step will be to see how quantitative density measures and other imaging biomarkers are associated with cancer risk, cancer subtype, and stage of diagnosis by race,” McCarthy says.

References

1. McCarthy AM, Keller B, Synnestvedt, et al. Racial differences in quantitative measures of area and volumetric breast density. Presented at: AACR Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA. Abstract 6580.

2. Weigert JM. The Connecticut experiment: 4 years of screening women with dense breasts with bilateral ultrasound. Presented at: San Antonio Breast Cancer Symposium; December 9-13, 2014; San Antonio, TX. Abstract S5-01.