High breast density is a risk factor for developing breast cancer, but it does not affect a patient’s risk of death, according to a recent study.

To examine the relationship between breast density and risk of death from breast cancer, researchers looked at medical records from more than 9,000 patients with breast cancer. After accounting for age, body mass, treatment, and other factors that could influence the risk of death, the researchers found that women with dense breasts were not more likely to die from the disease than women with less dense breasts during nearly seven years of follow-up.

The researchers also found that patients with breast cancer who had the least dense breasts had an increased risk of death from breast cancer if they had large tumors or were obese. Obesity is a known risk factor for death from breast cancer. The researchers hypothesized that the fat content of the breast might enhance the obesity-related mechanisms that heighten tumor aggressiveness in breast cancer. Further studies are being conducted to determine the biology of breast density.