While getting a mammogram is a good way to detect the possibility of breast cancer, it can also detect something else: dense breast tissue. In fact, dense breast tissue is a finding exclusive to a mammogram, wherein certain parts of the breast appear light gray or white, making it harder to detect any present abnormalities, according to the Susan G Komen breast cancer research organization.
Additionally, the American Cancer Society (ACS) notes that women with dense breast tissue have a higher risk of breast cancer than those with less dense breast tissue, although why that may be is unclear. What else should you know about dense breast tissue, and how do you properly screen for breast cancer if you have it? Read on to learn more.
Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue (also known as ducts and lobules), says the ACS. The fibrous tissue helps to hold the breast in place while the glandular tissues are what produce and store breast milk. Interspersed within these structures is the fatty tissue. The fibrous and glandular tissues are collectively referred to as dense tissue, and those with dense breasts have more of these two kinds in relation to the amount of fatty tissue present, says the National Cancer Institute (NCI).
Anita Johnson MD, FACS, breast cancer surgical oncologist at the Cancer Treatment Centers of America, says that dense breast tissue is "tissue on the mammogram that is hard to see." In order to assess mammographic density (the term commonly used to describe the percentage of dense tissue in the breasts), clinicians will look at a patient's mammogram and use BI-RADS, the Breast Imaging Reporting and Data System. Mammographic density is scored on a range from 1 to 4, wherein a mammographic density of level 1 indicates that the breast is composed almost completely of fatty tissue and level 4 describes breasts with 75% or more of the tissue present being dense tissue, according to a 2018 review article in the journal Breast Cancer.
A higher mammographic breast density is associated with a higher risk of breast cancer in two ways. First, it can reduce the sensitivity of a mammogram, potentially obstructing abnormalities. Second, it has been found to be an independent risk factor for development of breast cancer, and studies have shown a positive correlation between higher mammographic density and incidents of breast cancer. A 2012 study in the Journal of the National Cancer Institute found that those with higher breast density are more likely to have interval cancer (cancer that presents because of symptoms during the time between regular screening), so it's important to make regular screening appointments.
Higher mammographic breast density is associated with postmenopausal use of hormone replacement therapy and low body mass index, according to the NCI. Studies have also shown that it's commonly associated with genetics. A nearly two-decades-old study of twins published in the New England Journal of Medicine found that mammographic breast density at a given age has high heritability.
Another important factor is age. Susan Brown, MS, RN, and director of the health information center at Susan Komen tells Health that findings of a high breast density is more common for those ages 44 and younger who have gotten mammograms (many don't start getting mammograms until the age of 40). "As one ages, their breast density is lowered," she says. However, those who are post-menopausal and taking estrogen and progestin have also been found to be at increased risk, although an older study in the Journal of the National Cancer Institute states that only taking estrogen (without progestin) may not be associated with increased breast density.
According to Dr. Johnson, dense breast tissue is not something you can get rid of, and she also explains that not everyone who has it will develop cancer. It is advised that patients who are at risk and those who are above the age of 40 get their routine mammograms. Since breast density has the capability to obscure tumors, mammogram centers are now obligated by an FDA proposal to inform patients of their findings.
Knowing if you have a higher mammographic density is important, as Dr. Johnson advises being proactive and making an appointment with your provider to talk about a plan of action. "Know your family history, talk to your primary physicians about additional imaging," she says. This is especially important, given the higher risk associated with interval cancers.
Brown mentions that this is still an area of research. "There are no guidelines on what to do with the information on increased breast density. There are currently studies looking at whether 3-D mammography is better than 2-D in saving lives. But in most cases, ultrasound and breast MRI are recommended to further assess the situation," she explains. Dr. Johnson advises talking with your physician about additional imaging, perhaps especially if there's a family history of cancer.
Further, the American College of Obstetricians and Gynecologists say that "screening mammography remains the most useful tool for breast cancer detection and consistently has demonstrated a reduction in breast cancer mortality."
Dr. Johnson also reminds us of the bottom line, which is that early detection matters. While several guideline groups mention that the decision to start getting regular mammograms between the ages of 40 to 49 is a personal choice, Dr. Johnson advises making an appointment, especially if you are at an increased risk.