Mammogram: Can it find cancer in dense breasts?

Dense breasts can make traditional mammograms more difficult to interpret. But this doesn't mean a traditional mammogram is useless for detecting cancer or other breast abnormalities in women with dense breasts.

Breast tissue is composed of non-dense tissue (fat) and dense tissue (glands, ligaments and stromal tissue). The relative ratio of density to fat differs among women.

Dense breast tissue appears as a solid white area on a mammogram film, and fat appears as a dark area. Mammogram X-rays do not penetrate — or "see through" — dense tissues as well as they do through fat. So, in women with dense breasts, mammograms are more difficult to interpret. Tumors also are dense tissue and appear as solid white areas on the film. This can make it more difficult to detect a tumor in dense breasts because it looks a lot like the dense tissue that surrounds it. It's not clear why some women have more dense breast tissue than do others.

A study published in 2005 found that newer digital mammography does a better job detecting cancer in dense breasts than does traditional mammography. However, because of the newness of digital mammography, it isn't widely available yet.

If you have dense breasts and your doctor detects a breast lump, he or she may recommend further evaluation of the lump — even if a mammogram is interpreted as normal. Additional tests may include:

• Ultrasound
• MRI
• Removal of a small amount of tissue (biopsy) for examination under a microscope