What a New Meta-Analysis Reveals About Breast Density, Mammography and MRI Screening

Assessing data from 386,590 women, researchers noted that women with extremely dense breast tissue have more than double the risk for breast cancer in comparison to women with average breast density and nearly four times the risk of women with extremely fatty breast tissue.

In a newly published meta-analysis examining breast density and current breast cancer screening modalities, researchers reaffirmed the significant link between extremely dense breasts and breast cancer risk and suggested that supplemental magnetic resonance imaging (MRI) screening may be advantageous in this higher-risk patient population.

In their review of nine observational digital mammography studies and data from a total of 386,590 women who had breast imaging, researchers examined the correlation between breast cancer risk and mammographic density assessed via the Breast Imaging Reporting and Data Systems (BI-RADS) 5th edition. According to the meta-analysis, published in The Breast, the cohorts in the included studies were predominantly comprised of women between 50 and 70 years of age with median ages ranging between the early and late fifties.

Women with extremely dense breast tissue (BI-RADS D) had a 2.11-fold increased risk for breast cancer in comparison to women with scattered dense breast tissue or average breast density (BI-RADS B), according to the study. After adjustments for the covariates of age and body mass index, researchers said a subsequent sensitivity analysis revealed a 1.83-fold higher risk for breast cancer for the BI-RADS D group in comparison to those in the BI-RADS B group.

“(Drawing from research involving current widely used breast density measurement tools), this systematic review, based on data of 386,590 women, provides further evidence that having extremely dense breast tissue (BI-RADS density D) is significantly associated with increased breast cancer risk compared to having scattered dense breast tissue (BI-RADS density B),” wrote study co-author G.H. de Bock, Ph.D, who is affiliated with the Department of Epidemiology at the University Medical Center Groningen and the University of Groningen in the Netherlands, and colleagues.

(Editor’s note: For related content, see “New Mammography Study Examines Association Between Breast Density Changes and Breast Cancer Risk” and “Ten Key Considerations with Breast MRI.”)

The researchers also found that women with BI-RADS D had a 3.89-fold increased breast cancer risk in comparison to women in the BI-RADS A category (extremely fatty breast tissue). Noting that this risk estimate is lower than estimates from previous studies, de Bock said this could be attributed to different reference groups and density classifications used in studies as well as the advent of digital mammography.

The study authors note that the BI-RADS lexicon is reliant upon subjective assessments of qualitative breast density that may be affected by inter-reader variability and possible misclassification. While studies have demonstrated higher accuracy and detection rates with digital mammography in comparison to screen film mammography, de Bock and colleagues noted a “slightly weaker” association between breast density and cancer risk with digital mammography in comparison to screen film mammography.

Acknowledging a reduced sensitivity of mammography for women with dense breasts, de Bock and colleagues “strongly advise” MRI screening in this higher risk population.

“It can be questioned whether a twofold risk (of breast cancer) is strong enough to advocate breast MRI for women with dense breasts,” noted Dr. de Bock and colleagues. “This risk estimate is equal to the lowest risk estimate associated with a strong family history of breast cancer, which is associated with a two- to threefold increased breast cancer risk, and is therefore considered as substantial, also given the high lifetime risk for breast cancer in general population women of about 15 percent.”

In regard to study limitations, the authors noted that only nine studies were included in the meta-analysis and acknowledged variation between the studies with methodology, breast cancer outcomes and whether ductal carcinoma in situ (DCIS) cases were included in studies.