The breast is composed of three types of tissue – fibrous, glandular, and fatty. Breast density reflects the amount of fibrous and glandular tissue in the breasts as seen on mammograms.
–        10% of women will have almost entirely fatty breast tissue
–        40% of women will have scattered dense glandular and fibrous tissue
–        40% of women will have heterogeneously  dense tissue with many areas of glandular and fibrous tissue
–        10% of women will have extremely dense tissue
So approximately 50% of women will receive a mammogram report stating that the breasts are dense.