All breasts contain ducts and their milk-producing glands, fibrous tissue, and fat. The glands and fibrous tissue (or “fibroglandular” tissue) are referred to as “dense tissue”. Each woman’s breasts are different from the next and contain a unique mix of fatty and dense tissue. Some women have very little dense tissue compared to fatty, some have a lot, and most are in between. A woman may be considered to have “dense breasts” based on the amount of dense tissue she has, which is determined by a mammogram (see FAQ #3 for an explanation of how breast density is categorized from a mammogram).
Dense breasts are normal, and not a diagnosis, illness, or condition. Dense breasts are important for two reasons:
1. Dense tissue can hide cancer on a mammogram.
2. Having dense breasts increases a woman’s risk for breast cancer.
Dense tissue blocks x-rays and therefore shows up light gray or white on a mammogram. Most breast masses (whether due to cancer or not) also block x-rays and appear light gray or white on a mammogram, making them difficult to see in dense tissue, where they occur more often. Fatty tissue allows more x-rays to penetrate and therefore shows up as dark gray or black on a mammogram. Breast masses (whether due to cancer or not) are easier to see in fatty tissue.
Diagrams of the normal breast. Left: The normal breast is composed of milk-producing glands at the ends of ducts that lead to the nipple. Fibrous tissue surrounds the glands. There is layer of fat just beneath the skin. Often a few lymph nodes and the underlying muscle are seen near the underarm (axilla). Right: On a mammogram, fat appears dark gray, glands and fibrous tissue (dense tissue), as well as muscle, and lymph nodes appear light gray or white. Masses due to cancer also appear white.Browse All Patient FAQ's