Approximately 40-50% of women over the age of 40 are considered to have dense breasts. The breast is normally composed of fat and glandular tissue – the higher the proportion of glandular tissue, the denser the breast. Dense breast tissue appears “white” on a mammogram, and the challenge is that cancers also will often appear as a white mass on mammogram. “Lumpy” breast tissue is not the same as dense breast tissue – density is determined by the appearance on a mammogram, not by feel.Approximately 10-20% of breast cancers are missed by standard mammography, and that percentage can approach 40-50% in women with dense breasts. In addition, women with dense breasts have an increased risk of developing breast cancer.here are many factors that influence breast density including age, hormone levels, genetics, age at first pregnancy, number of pregnancies, use of hormone replacement therapy, and overall body weight – just to name a few. Younger women naturally have denser breast tissue, but that does not mean that all young women are at increased risk for breast cancer. The risk of breast cancer increases with age, and it is hard to sort out when the increased risk develops in relation to breast density.Over the past several years, there has been an increased awareness of the significance of dense breasts. Mammogram reports contain a notation of breast density, but the “layperson letter” that the patient receives does not always contain this information.