Dense Breast Tissue: What It Is & What It Means About Cancer Risk

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  • Breast Anatomy

    Breast Anatomy

    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 raised area on the outside is the nipple. Surrounding the nipple is darker colored skin called the areola.

    The inside is made up of glandular, fat (adipose), and supportive tissue. A system of lymph nodes, called the internal mammary chain, runs through the center of the chest.

  • Glandular Tissue

    Glandular Tissue

    Glandular tissue consists of a complex network designed to carry milk to the nipple. This glandular part of the breast is divided into sections called lobes. Within each lobe are smaller bulbs, called lobules, which produce milk. Milk travels through small ducts, which come together and connect into larger ducts designed to hold the milk. The ducts end at the nipple. 

  • Supportive Tissue

    Supportive Tissue

    The rest of the breast consists of fatty tissue and connective tissue that provide shape and support. There are nerves, blood vessels, and lymphatic vessels. Breast tissue extends from the breastbone near the middle of the chest all the way to the armpit area.

    The lymph vessels of the breast drain excess fluid and plasma proteins into lymph nodes. Most of this drainage goes into nodes in the armpit, and the rest goes to nodes located in the middle of the chest.

  • What Is Breast Density?

    What Is Breast Density?

    Breasts are considered dense when there is more glandular tissue than fatty and supportive tissue. Radiologists can see density on mammograms because glandular (dense) tissue looks white on a mammogram. Fatty tissue is non-dense, and appears black on a mammogram.

    Having dense breasts is common in younger women and women of childbearing age. According to Oxford Journal of Medicine, nearly 40 percent of women in the United States have dense breasts. Of those with dense breasts, 10 percent have what is known as level 4 density. Studies have shown that these women have a higher risk for developing breast cancer. As a woman ages and approaches menopause, breast density often decreases. 

  • Breast Density and You

    Breast Density and You

    Many states, including California, Virginia, and New York now require radiologists to contact a woman if her breasts are dense. The law is designed to improve breast cancer detection by notifying a woman that mammography may not be as effective for her as other detection tools are. But this doesn’t necessarily mean her risk of cancer is greater.

    According to Dr. Carol Lee, a radiologist with Memorial Sloan Kettering, this notification is meant to facilitate communication between a woman and her doctor in order to discuss risk factors that might call for other types of testing.

  • Breast Density and Mammography

    Breast Density and Mammography

    Mammography may be unable to discern the presence of early cancers in such breasts because both cancer and dense breasts appear white. Although digital mammograms have better resolution in the context of high breast density, all mammograms are limited in their ability to identify cancers in dense breasts. 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.

  • Breast Density and Cancer Risks

    Breast Density and Cancer Risks

    While dense breasts make mammograms harder to interpret, studies also 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.

  • What Should a Woman with Dense Breasts Do?

    What Should a Woman with Dense Breasts Do?

    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. Women on hormone therapy may want to discuss this with their doctor, as there is evidence that hormones may also increase cancer risk.

  • Statistics Alone Can Be Misleading

    Statistics Alone Can Be Misleading

    While these statistics may be frightening, keep in mind that these studies describe the risk for those in the highest density category (the upper 10 percent) by comparing them to those in the lowest density category (the lowest 10 percent). The risks don’t necessarily apply to those in the middle (80 percent). Generally, breast density is not a major cancer risk factor for most women.

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