Increased Risk of Death Not Seen in Breast Cancer Patients with High-Density Mammograms

High mammographic breast density, which is a marker of increased risk of developing breast cancer, does not seem to increase the risk of death among breast cancer patients, according to a study led National Cancer Institute (NCI; Bethesda, MD, USA) scientist. The research was conducted in collaboration with investigators from the NCI-sponsored Breast Cancer Surveillance Consortium (BCSC).

In the study led by Gretchen L. Gierach, PhD, of over 9,000 women with a confirmed diagnosis of breast cancer, high mammographic density was not associated with the risk of death from breast cancer or death from all causes combined. The study appeared August 20, 2012, in the Journal of the National Cancer Institute.

Although high mammographic breast density is a well-established risk factor for developing breast cancer, it was unclear prior to this study whether breast density is also associated with the risk of death among women diagnosed with breast cancer. To address this question the scientists analyzed data from the BCSC, a population-based registry of breast imaging facilities in the United States. The scientists restricted their analysis to five BCSC registries that consistently collect data on body mass index (BMI). BMI is a poor prognostic factor for breast cancer inversely related to breast density and could potentially affect associations between density and breast cancer death.

Patients included in the study were 30 years or older at breast cancer diagnosis, which occurred primarily between January 1996 and December 2005. The patients were followed, on average, for 6.6 years, at which time 1,795 deaths were reported, including 889 from breast cancer and 810 from other causes. To analyze breast density, the scientists used the most widely available measure of breast density currently in clinical use, a score known as the Breast Imaging-Reporting and Data System score, which is given by a radiologist based on visual review of a mammogram. Data on tumor characteristics and other personal and health factors were also analyzed.

The analysis of mammographic density showed that breast cancer patients with high-density breasts did not have a higher risk of death from breast cancer than patients with lower density breasts, after adjusting for other health factors and tumor characteristics. The lack of an association between mammographic breast density and breast cancer death is consistent with findings from an earlier, smaller study that examined this association.

This study also found an increase in risk of breast cancer death associated with lower breast density among specific subgroups, particularly breast cancer patients who are obese. The authors speculate that one possible explanation for the increased risk associated with low breast density among some subgroups is that breasts with a higher percentage of fat may provide a tumor microenvironment that facilitates cancer growth and 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," said Gierach. "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."

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