Understanding Dense Breasts and Cancer Risk
- As journalist Katie Couric, a breast cancer survivor who has dense breasts, is celebrating her 68th birthday, we’re reminded of the importance of breast cancer screenings for women— as a new study is suggesting there’s a connection between breast density changes and breast cancer risk.
- The new study, which says that as a woman’s breast density increases over time, so does her breast cancer risk, comes just months after the U.S. Food and Drug Administration (FDA) started requiring mammogram reports to include a section that informs women about their breast density.
- Women with dense breasts are at a higher risk for developing breast cancer because dense breast tissue can mask potential cancer during screening.
- While mammograms are extremely valuable for breast cancer screening, more effective screening methods exist for women with dense breasts.
- 3D mammograms, breast ultrasound, breast MRI, and molecular breast imaging are options for women with dense breasts for a more precise screening. It is important to ask your doctor about your breast density and cancer risk.
New research has concluded that women whose breast density increased over time were 1.6 times more likely to be diagnosed with breast cancer—serving as a reminder for women with dense breasts, like famed journalist Katie Couric, to follow necessary screening guidelines.
Read More“Future risk of breast cancer was found to vary in these groups. Increasingly dense or persistently dense breasts were associated with a higher risk,” the study authors explained.
“Changes in breast density over time should be carefully considered during breast cancer risk stratification and incorporated into future risk models.”
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The types of breast tissue women in the study had, consisted of “almost entirely fat, scattered fibroglandular density, heterogeneously dense, and extremely dense.”
Women with breast density that increased over the years had an increased cancer risk and women with denser breasts that decreased over time had either a consistent or somewhat less risk as time passed.
The study is suggesting that women with higher breast density had a heightened risk of breast cancer when compared to women with low breast density.
Additionally, women with constant high breast density were 3.07 times more likely to be diagnosed with breast cancer than those who had “consistently fatty breast tissue and a slightly decreasing trend in density.”
Meanwhile, the connection of dense breasts and cancer risk has been demonstrated time and again in several rigorous scientific studies. 1 in 6 women with dense breasts are at risk for breast cancer. Comparatively, 1 in 8 women with average breasts are at risk for this cancer. And the precise reason for this difference is not fully understood.
Researchers from Washington University School of Medicine in St. Louis and Brigham and Women’s Hospital in Boston also conducted a study to analyze this connected.
They recruited 947 women between November 2008 and October 2020. All women were cancer-free at the start of the study and received yearly or bi-yearly screening mammograms. Researchers tracked the women’s mammogram reports and breast densities over time.
All women experienced a decline in their breast density during the 12 years. Two hundred eighty-nine women developed breast cancer during this time. Those who developed cancer had a lower rate of decrease in breast density than those who did not. The researchers concluded that the rate of breast density changes may indicate future breast cancer risk.
New FDA Guidelines on Mammograms & Dense Breasts
For women with dense breasts, meaning they have more fibroglandular tissue and less fatty breast tissue, like Katie Couric, it can be more difficult for mammograms to locate breast cancer due to the dense tissues.
Thankfully, a new rule was put into effect on September 10, 2024, by the Food and Drug Administration (FDA), requiring women undergoing mammograms, which screen for breast cancer, to be notified of their breast density.
Helping Patients Better Understand Dense Breasts
- How to Avoid False Positive Cancer Results in Women With Dense Breasts: Ultrasounds Used in Addition To Mammograms
- I Have Dense Breasts. Do I Need a 3D Mammogram?
- Millions of Women With Dense Breasts — A New Congressional Law — What You Need to Know
- When You’re Getting a Mammogram, Ask About Dense Breasts
The rule calls for the mammography report to include a breast density assessment section. The report will have the following categories:
- “The breasts are almost entirely fatty.”
- “There are scattered areas of fibroglandular density.”
- “The breasts are heterogeneously dense, which may obscure small masses.”
- “The breasts are extremely dense, which lowers the sensitivity of mammography.”
The report will also explain if a woman’s breast tissue is dense, the dense breast tissue makes cancer more challenging to detect in a routine mammogram.
The dense tissue has a “masking effect on how well we can perceive cancer and find cancer on mammograms,” Dr. Cindy Ly, a radiology doctor at NYU Langone Medical Center, previously told SurvivorNet.
Understanding Your Mammogram Report and Breast Density
A radiologist reading mammograms categorizes breasts into four different categories using the Breast Imaging Reporting and Data System (BI-RADS), a classification system developed by the American College of Radiology (ACR). These include:
- Fatty breast tissue: These breasts are mainly composed of fat with very little dense tissue. Found in less than 10% of women, fatty breasts appear dark on mammograms.
- Scattered fibroglandular breast tissue: These breasts contain a mix of fatty and dense tissue (composed of glands and fibrous tissue). On a mammogram, they have dark areas (fatty tissue) intermixed with light areas (dense tissue). Around 40% of women have breasts that fall in this category.
- Heterogeneously dense breast tissue: This type of breast tissue has many areas of dense tissue and some areas of fat. Found in 40% of women, these breasts look mostly light, with some dark areas on a mammogram.
- Extremely dense breast tissue: Such breasts are almost entirely composed of dense glandular and fibrous connective tissues with very little fat. They are found in 10% of women and appear light on mammograms.
Your breasts are usually called dense on a mammogram report if they fall within the heterogeneously dense breast tissue or the extremely dense breast tissue categories.
WATCH: When You’re Getting a Mammogram, Ask About Dense Breasts
Katie Couric’s Breast Cancer Journey
Couric was diagnosed in June 2022 but revealed her cancer to the world during Breast Cancer Awareness Month in 2023. She was diagnosed with early-stage breast cancer, specifically stage 1A.
Her type was HER2/neu. According to the American Cancer Society, HER2 is a protein that helps breast cancer cells grow quickly. Breast cancer cells with higher than normal levels of HER2 are called HER2-positive.
“I was nervous about it. I waited a few days so I could process it and really understand what we were dealing with,” Couric said to “Today” at the time.
Dr. Michael Zeidman, assistant professor of surgery at Icahn School of Medicine at Mount Sinai in New York City, tells SurvivorNet that stage 1 is divided into two subcategories, 1a and 1b. Stage 1a breast cancer means the cancer hasn’t spread outside the breast. Stage 1b means there’s no tumor in the breast; instead, small groups of cancer cells are found in the lymph nodes. Stage 1b can also mean there’s a tumor in the breast and small groups of cancer cells in the lymph nodes. Stage 1 also means the cancer was caught very early, he says.
She underwent surgery and radiation therapy to treat the cancer a few months after her diagnosis.
RELATED: Millions of Women With Dense Breasts: A New Congressional Law What You Need to Know
During Couric’s cancer journey, she learned she had dense breasts. To help her navigate the challenges dense breast tissue brings during mammograms, Couric receives additional screening, which includes a breast ultrasound.
Additional screening methods are helpful for women with dense breasts because glandular tissue appears white on mammograms. Cancer and other abnormalities also exhibit a similar appearance. The “frosted glass” effect from the glandular tissue can thus mask cancerous areas, especially nascent ones.
Undetected, these cancers can progress, growing large and advanced. They will then likely require more intensive treatments to cure or can become incurable altogether.
Additional Screening for Dense Breasts
Women with dense breasts may not know they have it based on feeling alone. Breast density is determined by its appearance on a mammogram. Dr. Connie Lehman, the chief of the Breast Imaging Division at Massachusetts General Hospital, explains to SurvivorNet that fatty breast tissue appears gray on an X-ray.
Conversely, dense breast structures appear white during an X-ray. Cancers also appear white on an X-ray, meaning the dense breast structures can mask the possibility of cancer. Luckily, advanced mammograms exist to help doctors navigate this obstacle.
WATCH: 3D Mammograms explained.
“Digital mammography, it turns out, significantly improves the quality of the mammogram…It’s 3D or tomosynthesis mammography,” Dr. Lehman explains.
“This allows us to find more cancers and to significantly reduce our false-positive rate. With digital mammography 3D tomosynthesis, we’re taking thin slices through that breast tissue, like slices of a loaf of bread. We can look at each slice independently rather than trying to see through the entire thickness of the entire loaf of bread. So those thin slices help us find things that were hidden in all the multiple layers,” Dr. Lehman adds.
Additional testing can be considered for dense breasts, depending on a woman’s personal history, preferences, and her physician’s guidance. These tests include:
- 3-D Mammogram (Breast Tomosynthesis): This technology acquires breast imaging from multiple angles and digitally combines them into a 3D representation of the breast tissue. This allows physicians to see breast tissue architecture better, even in dense breasts. 3D mammograms are fast becoming the standard way of performing mammography.
- Breast Magnetic Resonance Imaging (MRI): An MRI machine uses magnets to create highly detailed, intricate images of the breast. These are mostly reserved for women with an extremely high breast cancer risk. Dense breasts alone may not be a valid reason to obtain a breast MRI. However, dense breasts in women with genetic mutations, like BRCA1 and BRCA2, or a strong family history of breast cancer could justify obtaining breast MRIs.
- Molecular Breast Imaging (MBI): MBI is a newer imaging technique that uses a radioactive tracer to detect breast cancer. It is beneficial for women with dense breasts. However, MBI is not as widely available as other screening methods.
With the help of the FDA’s new rule, facilities offering mammograms will need to inform patients about their breast tissue density and recommend they speak with a doctor to determine if further screening is necessary. There will be “uniform guidance” on what language to use and what details to share with the patient to make the communication clear and understandable.
WATCH: Breast Cancer Surgeon Lays Out Ways We Can Close the Gap in Racial Disparity.
The Exact Cause Of Dense Breasts In Not Fully Understood
Why certain women are born with dense breasts while others aren’t is not always known. However, it is likely that several factors contribute to a woman’s breast cancer density.
Genetics is a likely contributor to breast density. If women in your family have a history of dense breasts, you are more likely to have similarly dense breast tissue. However, genetics is not the only reason.
Levels of estrogen and progesterone, two hormones that are essential to female health and reproduction, may also influence breast density. Pre-menopausal women who tend to have higher levels of these hormones have denser breasts than post-menopausal women, who have lower hormonal levels. By extension, women who take hormone replacement therapies after menopause may unwittingly increase their breast tissue density.
Age is another determinant of breast density. Younger women tend to have denser breasts than older women. Body weight also impacts density, with women with lower body weight (by extension, low body fat percentage) possessing more dense breasts than those with higher body weight.
Additionally, it’s unknown whether women can directly change their breast density to decrease their risk for cancer.
There is evidence that diet and lifestyle factors influence breast density, with women with more body fat accumulating fat within their breasts, which lowers their breast density.
However, gaining weight just to decrease breast density may be counterproductive. Robust scientific studies have repeatedly shown that maintaining a healthy weight through diet and physical activity lowers the risk of any cancer. Thus, any benefit of a decrease in breast density through an increase in body fat is likely more than offset by the increased risk of cancer associated with being overweight or obese.
The Importance of Breast Cancer Screenings
Mammograms are used to screen for breast cancer. Women who haven’t gone through menopause are encouraged to get a mammogram annually between the ages of 45 and 54. If you have experienced menopause, you can get a mammogram every two years.
The U.S. Preventive Services Task Force recommends women begin screening for breast cancer at age 40. Women should talk with their doctor to learn about their cancer risk and assess when a good time is to start annual mammograms.
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“We all agree regular screening mammography saves lives,” Dr. Connie Lehman, a professor at Harvard Medical School, told SurvivorNet.
Suppose you fit into the high-risk category for breast cancer, meaning a close family relative has been diagnosed. People at higher risk may have the BRCA1 or BRCA2 gene mutation or had radiation to the chest area when they were young. In cases like this, people in the high-risk category should begin annual mammograms at 30 years old.
Contributing: SurvivorNet Staff
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