High Breast Density Does Not Predict Death among Breast Cancer PatientsHigh breast density is a strong risk factor for developing breast cancer, but it does not affect a breast cancer patient’s risk of death, according to a study recently published in the Journal of the National Cancer Institute.
Denser breasts have more glandular tissue (cells that produce milk during lactation) and supportive connective tissue than fatty tissue. Doctors use a scale called the Breast Imaging Reporting and Data System (BI-RADS) to classify breast density as observed on mammograms on a scale from 1 to 4, with 1 being the least dense and 4 the most dense.
To examine the relationship between breast density and risk of death from breast cancer, Dr. Gretchen Gierach and her colleagues from NCI’s Division of Cancer Epidemiology and Genetics and the NCI-sponsored Breast Cancer Surveillance Consortium (BCSC) examined medical records from more than 9,000 breast cancer patients collected by the BCSC.
After accounting for age, body mass, treatment, and other factors that could influence the risk of death, the researchers found that among women diagnosed with breast cancer, women with dense breasts were not more likely to die of the disease or of other causes than women with less-dense breasts during nearly 7 years of follow-up, on average.
Unexpectedly, the researchers observed that breast cancer patients with the least-dense breasts had an increased risk of death from breast cancer if they had large tumors or were obese. However, given that this result was based on relatively small numbers of women and has not been previously suggested by other studies, “these findings need to be replicated in larger studies,” said Dr. Gierach.
Obesity is a risk factor for death from breast cancer and is also inversely related to breast density. (That is, obese women are less likely to have dense breasts.) Therefore, obesity could affect associations between breast density and breast cancer death.
“We already know that obesity is a poor prognostic factor for breast cancer in general, but this particular analysis showed that the subgroup of women who were obese and had less-dense, fatty breasts were at greatest risk,” she explained. “Our hypothesis is that the fat content in the breast might be enhancing obesity-related mechanisms that heighten tumor aggressiveness in breast cancer. We are conducting studies to better understand the biology of breast density.”
This research was supported in part by grants from the National Institutes of Health (U01CA63740,U01CA86076, U01CA86082, U01CA63736, U01CA70013, U01CA69976, U01CA63731, U01CA70040, and HHSN261201100031C).