1. Breasts are made of fat and glands (that make milk) held together by fibrous tissue. The more glands and fibrous tissue that a woman has, the “denser” her breast tissue.

(Click images to enlarge)

2. Many women have dense breasts. This is normal and common. In fact, almost half (about 50%) of women over age 40 have dense breasts.

3. When radiologists review (look closely at) mammograms, they can see how dense the breasts are. In these four mammogram images, the dense tissue appears as white. Categories A and B are “not dense” breasts. Categories C and D are “dense” breasts.

4. Dense tissue appears as white on a mammogram. Cancer also appears as white. This makes it harder for radiologists to see a cancer in dense breasts. Because of this, cancers are often larger when found in women with dense breasts.

In these images, you can see how dense breasts can “hide” cancer.

5. Dense breasts are also a risk factor for breast cancer. A woman’s risk for breast cancer increases with the level of density in her breasts.