October is Breast Cancer Awareness Month. This month, we aim to raise awareness and action, support breast cancer survivors, and help women suffering from the disease by sharing relevant information. Since 1993, The Breast Cancer Research Foundation, a nonprofit organization, has been committed to achieving prevention and a cure for breast cancer by advancing the world’s most promising research. Recently, they launched a new study exploring the meaning of dense breast tissue. Dense breasts are associated with an elevated risk of developing breast cancer because the breast tissue can make it difficult for doctors to see abnormal growths in mammograms that may be cancer. But what does it mean to have dense breast tissue, and why is it important to know if you have it? BCRF explored this topic and highlighted research on improving breast cancer detection in women with dense breasts. See their findings below.
What’s dense breast tissue? According to BCRF, breasts are made up of different types of tissue: Fibrous or connective tissue that holds the breast in place; glandular tissue, which includes lobules and ducts that produce and transport milk; and fatty tissue that fills the space between fibrous and glandular tissue and helps give breasts their size and shape. Breast density measures how much fibrous and glandular tissue (referred to as fibroglandular tissue) there is in the breast relative to fat tissue. If you have higher breast density, your breasts comprise more fibroglandular tissue than fat. Dense breasts are normal and occur in nearly half of women over 40. On average, breast density is higher in women under 40 and tends to decrease as they age; 40 percent of women in their 50s and 25 percent of women aged 60 and over have dense breasts. According to the CDC, women are more likely to have dense breasts if pregnant or breastfeeding, take hormone replacement therapy, or have a lower body weight.
On average, breast density is higher in women under 40 and tends to decrease as women get older.
Why is it important to know if you have dense breasts?
Breast density is one factor associated with an elevated breast cancer risk. Breast cancer is known to develop in glandular tissue, so having more tissue may allow abnormal cells to grow. Higher breast density can also make it more challenging for radiologists to see abnormal growths since they both appear white on a mammogram, as dense breast tissue can effectively “cloud” the mammogram and increase the likelihood that a potentially cancerous growth or tumor is missed.
How is dense breast tissue categorized?
Doctors use a system developed by the American College of Radiology (ACR) called Breast Imaging Reporting and Data System (BI-RADS) to interpret and report standardized mammogram findings. It is subjective, so doctors increasingly use automated software to assist in the classification process. BI-RADS classifies dense breasts into four categories:
Category A is for breasts composed entirely or almost entirely of fatty breast tissue. The mammogram from this breast will appear primarily dark gray or black and may have small amounts of dense tissue that appear light gray or white. About 10 percent of women fall into this category.
Scattered areas of dense tissue define category B. A Category B mammogram will have light and dark gray or black areas. Tumors can be obscured in regions of the breast that appear dense. About 40 percent of women fall into category B.
Category C is comprised of heterogeneously dense breasts. On a mammogram, these breasts will appear mostly light gray or white. About 40 percent of women fall into this category.
Category D is defined as highly dense breasts. Most of the breast comprises dense breast tissue, and the mammogram appears almost entirely white. Ten percent of women fall into Category D.
Women in categories C and D are considered to have dense breasts.
How should dense breasts be screened for breast cancer?
Dense breasts make standard mammograms—also called 2D mammograms because they are a two-dimensional image of a three-dimensional breast—more challenging for radiologists to spot potential cancer. In addition, many women receive 3D mammograms (also called tomosynthesis) as part of their standard screening, which has improved breast cancer detection in women with heterogeneously dense breasts. Still, results are mixed in women with extremely dense breasts.