A study conducted by researchers from the National Cancer Institute, part of the National Institutes of Health, found that high mammographic density in women with breast cancer was not associated with an increased risk of death from the disease. Mammographic density refers to the amount of white area seen on a mammogram – the more white, the higher the density of the breast.
Breasts with higher mammographic density typically have more glandular and connective tissues, called fibroglandular tissue, than fatty tissue (which looks black on a mammogram). Fibroglandular tissue blocks the passage of x-rays used in mammograms, producing the white areas. The darker areas of the mammogram, where the x-rays pass through the breast more completely, are due to fatty areas.
Reason for the Study
High mammographic density is a recognized risk factor for developing breast cancer. Researchers sought to explore whether the same high density was associated with an increased risk of death in women already diagnosed with breast cancer.
Researchers at NCI collaborated with peers at the Breast Cancer Surveillance Consortium, an NCI-sponsored registry of mammography facilities in the United States. Using data from BCSC, the investigators analyzed the cases of 9,232 women diagnosed with primary invasive breast cancer between 1996 and 2005.
The women included were age 30 or older at diagnosis. Their progress was followed for an average of 6.6 years. Breast density was measured using the Breast-Imaging Reporting Data System Score, a score ranging from 1 to 4 used by radiologists in interpreting mammograms. Other factors, such as personal and health factors, body mass index and tumor characteristics were also tracked during the study.
The data analysis showed that women with high mammographic density were not at higher risk of death from breast cancer than women with lower mammographic density, independent of other issues that may influence the risk for death, such as health factors and tumor characteristics.
Further analysis found an association between low mammographic density and risk of death from breast cancer among women who were classified as obese or had tumors 2.0 centimeters or larger. Researchers suggest that women with lower breast density who are obese have breasts with a higher percentage of fat, which may provide a better environment for tumor growth.
What This Means for You
The study results suggest that risk factors for developing breast cancer may not always increase the risk of death from breast cancer in women already diagnosed. It is important to note that the participants were followed for about six-and-a-half years, which may not be long enough to track their long-term outcome after treatment. The findings should prompt further study of the reasons some breast cancers are more likely to lead to death than others.
Despite the results of this study, high breast density does make it harder for doctors to detect breast cancer using mammograms. Current research is exploring better detection techniques for women who are at high risk of breast cancer because of high breast density.
If you have low mammographic density and are overweight, talk with your doctor about maintaining a healthy weight. No matter what your health status, getting exercise and eating well can improve your overall health and sense of well-being. For ideas to discuss with your doctor, visit our section on quality-of-life issues.
Gierach, Gretchen L., Ichikawa, Laura et al. Relationship between Mammographic Density and Breast Cancer Death in the Breast Cancer Surveillance Consortium. J Natl Cancer Inst (2012) 104 (16): 1218 – 1227.