One of the important variable characteristics in breast anatomy and physiology is breast tissue density. The density of breast tissue is derived from the ratio of fatty tissue to glandular (dense) tissue and varies greatly from woman to woman and sometimes year to year. The fact that dense breast tissue lowers the accuracy of mammograms has been recognized for some time. However, that reduction in accuracy should in no way serve as a reason for women with dense breast tissue to forgo their annual mammogram. For consistency, the American College of Radiology has 4 grades of breast composition to describe the breast density of all patients using the following patterns below.
Grade A. The breast is almost entirely fat (less than 25% glandular)
Grade B. There are scattered fibroglandular densities (approximately 25% - 50% glandular)
Grade C. The breast tissue is heterogeneously dense, which could obscure detection of small masses (approximately 51% - 75% glandular)
Grade D. The breast tissue is extremely dense. This may lower the sensitivity of mammography (greater than 75% glandular)
The assignment of a breast density grade by a radiologist when your mammogram is interpreted is often a “subjective” determination and could change from year-to-year with little actual change in density.
For a more extensive discussion on the anatomy and physiology of dense breast tissue, how it can change and how it may affect ones risk for breast cancer please follow the link below.
For a more scientific exploration of breast density and its relevance as a possible independent risk factor for breast cancer, please view the articles listed below.