Breast density is a measure that compares the amount of fat and the amount of tissue that make up the breast. Less-dense breasts have more tissue and less fat. More-dense breasts have more tissue and less fat.
High breast density is common. Between 40 and 50 percent of women aged 40 to 74 in the U.S. have dense breasts. Many factors can affect breast density including age, weight, genetics, family history and having fewer children, among others.
Studies have consistently found that women with high breast density have around a four to five times higher risk of breast cancer compared to women with low breast density. However, it is not really understood why breast density increases risk, or if there are any steps that women can take to directly lower the risk related to high breast density.
One concern with breast cancer screening in women with dense breasts is that some tumors may not show up well on mammograms. The denser the breast, the harder it can be to find tumors. Because of this, new methods to better detect breast cancer in dense breasts are being developed and tested.
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