High mammographic breast density is not related to the risk of dying from breast cancer, as reported in the Journal of the National Cancer Institute by Gretchen L. Gierach, PhD, MPH, of the Division of Cancer Epidemiology and Genetics at the National Cancer Institute in Maryland and colleagues.

Elevated mammographic breast density is one of the strongest risk factors for non-familial breast cancer. The study sought to understand if a higher density indicates a lower chance of survival in breast cancer patients.

The study used data from the US Breast Cancer Surveillance Consortium and examined 9,232 women with a diagnosis of primary invasive breast carcinoma between 1995 and 2005. The patients had an average follow-up of 6.6 years. Relationships between mammographic breast density and the risk of death from breast cancer and from all causes were studied. The researchers measured mammographic density with the Breast Imaging Reporting and Data System density classification.

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Density does not influence the risk of death once the disease has developed, according to the researchers. They wrote, “It is reassuring that elevated breast density, a prevalent and strong breast cancer risk factor, was not associated with risk of breast cancer death or death from any cause in this large, prospective study.”

Nonetheless, an association was found between low density and increased risk of breast cancer death among obese patients, or those diagnosed with large or high-grade tumors. The authors explained, “One explanation for the increased risks associated with low density among some subgroups is that breasts with a higher percentage of fat may contribute to a tumor microenvironment that facilitates cancer growth and progression.”

The research team stated that their findings highlight the need to further investigate “possible interactions between breast density, other patient characteristics, and subsequent treatment in influencing breast cancer prognosis.”