Breast Density Plays a Role in Risks for Breast Cancer

Before defining dense breast tissue, it’s important to understand the structures of the breast. The main function of breasts is to make milk for breastfeeding a baby. The inside is made up of glandular, fat, and supportive tissue. A system of lymph nodes, called the internal mammary chain, runs through the center of the chest.

Breasts are considered dense when there is more glandular tissue than fatty and supportive tissue. One way to measure breast density is the thickness of tissue on a mammogram. Another categorizes breast patterns into four types depending on which type of tissue makes up most of the breast. Still, no one method of measuring breast density has been agreed upon by doctors. Breast density is not based on how your breasts feel during your self-exam or your doctor's physical exam. Dense breasts have more gland tissue that makes and drains milk and supportive tissue (also called stroma) that surrounds the gland. Breast density can be inherited, so if your mother has dense breasts, it's likely you will, too.

Research has shown that dense breasts:

  • can be 6 times more likely to develop cancer
  • can make it harder for mammograms to detect breast cancer; breast cancers (which look white like breast gland tissue) are easier to see on a mammogram when they're surrounded by fatty tissue (which looks dark).

According to the National Cancer Institute, about 10 to 20 percent of cancers are missed by mammography. That percentage can approach 40 to 50 percent in women with dense breasts.

Studies show that women whose breasts are denser have a four to six times greater risk of breast cancer. This has puzzled researchers because these women are typically younger, and breast cancer is more commonly found in older women.

One thought is that women with dense breasts have a higher proportion of ducts and lobes and thus have a higher risk. Cancer arises in the lobes and ducts. But this is uncertain, and researchers are still studying this concept.

Women should ask their doctors if their breasts are dense and discuss their cancer risks. Those who have a family history or lifestyle risk of cancer may want to explore other testing options like ultrasound or MRI. These tests can sometimes be more helpful than a mammogram in evaluating a woman who has very dense breasts.

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Talk to Dr. Strebel or Dr. Grolle at your next appointment. They can help you decide which tests are right for you.