Rebecca Zuurbier, MD, Sibley Memorial Hospital, examines a digital mammogram of a dense breast and points to a potential cancer. Source: National Cancer Institute

High mammographic breast density is a marker of increased risk for developing breast cancer, but, according to research published Aug. 20 in the Journal of the National Cancer Institute, high density does not seem to increase the risk of death among breast cancer patients.

The study, conducted by Gretchen L. Gierach, PhD, of the National Cancer Institute, part of the National Institutes of Health, and colleagues did find, however, that higher risk of breast cancer death is associated with lower breast density in certain subgroups, particularly obese cancer patients. Gierach and colleagues wrote that the results “raise additional questions regarding possible interactions between breast density, other patient characteristics, and subsequent treatment in influencing breast cancer prognosis.”

The authors evaluated the relationship between mammographic breast density and risk of breast cancer death by studying 9,232 women from the U.S. Breast Cancer Surveillance Consortium. All women were diagnosed with invasive breast carcinoma between 1996 and 2005, and patients were followed for an average of 6.6 years. Analysis was restricted to five registries that collected data on body mass index (BMI), since BMI is inversely related to breast density and could affect associations between density and breast cancer death.

Gierach and colleagues reported that a total of 1,795 women died, 889 of whom died of breast cancer. Using the Breast Imaging Reporting and Data System (BI-RADS) mammographic density classifications, the analysis showed that breast cancer patients with high-density breasts were not at a higher risk of death from breast cancer than patients with lower breast density.

A stratified analysis found similar results in many of the study subgroups, except obese women and women who had tumors of at least 2 cm. In both groups, low density was associated with an increased risk of breast cancer death. In speculating about the explanation for increased risks among obese patients, the authors noted that a higher percentage of fat may provide an environment for tumor growth and cancer progression.

“Overall, it was reassuring to find that high mammographic breast density, one of the strongest risk factors for breast cancer, was not related to risk of death from breast cancer or death from any cause among breast cancer patients,” Gierach said in a release. “Given that we identified subsets of women with breast cancer for whom low density was associated with poor prognoses, our findings underscore the need for an improved understanding of the biological components that are responsible for breast density.”

A statement issued by the American College of Radiology (ACR) hailed the study as good news for women and called the results “reassuring.”

“Although they are at a small increased risk of developing breast cancer compared with women with fatty breasts, the good news is that they are not at increased risk of dying from breast cancer when compared to women with mostly fat in their breasts,” wrote the ACR.