- Breast density refers to the composition of breast tissue and is determined through mammograms.
- Women with dense breasts are at a higher risk for developing breast cancer.
- Breast density changes over time, and the rate of density change may indicate future breast cancer risk. In a new study, women who developed cancer had a lower rate of decline in breast density compared to those who did not. Thus, researchers concluded that the rate of breast density changes may indicate future breast cancer risk.
- It is unclear whether women can directly change their breast density to decrease their cancer risk.
- Mammograms are still valuable for detecting breast cancer in dense breasts, and newer technologies like 3D mammograms are more effective.
- Additional tests like breast ultrasound, breast MRI, and molecular breast imaging may be considered for women with dense breasts, but they have their own risks and may not reduce the risk of dying from breast cancer.
- It is important to discuss breast density, cancer risk, mammogram frequency, and additional testing options with a healthcare provider.
What Is Breast Cancer?
After skin cancer, breast cancer is the second most prevalent cancer among women in the United States (US). The American Cancer Society (ACS) anticipates that approximately 300,000 new cases of breast cancer and around 55,000 new cases of ductal carcinoma in situ (DCIS), a precursor to breast cancer, will be diagnosed in the US in 2023. Approximately 43,000 deaths are expected to occur due to this disease during this year.
What Is Breast Density? It's Not Something You Can FeelRead More
Your Mammogram Report May List Your Breast DensityA 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 are breasts that are mostly composed of fat with very little dense tissue. Found in <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 along with 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 fully composed of dense glandular and fibrous connective tissues with very little fat. They are found in 10% of women and appear very light on a mammogram.
Your breasts will usually be called dense on a mammogram report if they fall within the heterogeneously dense breast tissue or the extremely dense breast tissue categories.
It is important to emphasize that dense breasts are not an abnormality. They are a natural, normal variation of breast tissue.
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.
Your Breast Density: Why Does It Matter?
Women with dense breasts are at a higher risk for developing breast cancer. This connection 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. The exact reason for this difference is not fully understood. It is likely due to several factors, including but not limited to:
- Dense breasts contain significantly more glandular tissue than breasts that are not dense. In a normal breast, glandular tissue produces milk during breastfeeding. This tissue is much more active than fat tissue, which puts it at an increased risk of turning into cancer. Thus, the more glandular tissue a woman has, the more she is at risk for developing breast cancer.
- Moreover, 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 when they are nascent. Undetected, these cancers can progress, growing large and advanced. They will then likely require more intensive treatments to cure or can become incurable altogether.
Breast Density Changes Over Time. This May Change Your Cancer Risk.
While the connection between breast density and cancer is well-known, the effect of changes in breast density with time on cancer risk is less so. Researchers from Washington University School of Medicine in St Louis and Brigham and Women's Hospital in Boston analyzed this connection in a new study.
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. Their mammogram reports noted their breast densities, giving researchers a way to track it over time.
All women experienced a decline in their breast density over this time. 289 women developed breast cancer during this time. Those who developed cancer had a lower rate of decline in breast density compared to those who did not. Thus, The researchers concluded that the rate of breast density changes may indicate future breast cancer risk.
Can I Reduce My Breast Density To Decrease My Cancer Risk?
The jury is still out on 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.
Are Mammograms For Dense Breasts Different Than Regular Breasts?
Dense breasts make it challenging for doctors to detect cancers on mammograms. Yet mammograms continue to be an invaluable first step in managing your breast cancer risk. In fact, they are the only cancer screening test that has been demonstrated to decrease the risk of death from breast cancer. Mammogram technology has also evolved over time, with modern versions of the technique better able to detect cancers even in dense breasts.
Still, additional testing can be considered for dense breasts, depending on a woman's personal history, preferences, and her physician's guidance. These tests include:
- Breast ultrasound (US): Though routinely used to investigate areas of concern on mammograms, an US can also be used to supplement a regular mammogram in women with dense breasts.
- 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 better see breast tissue architecture, 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 who have an extremely high risk of breast cancer. 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 especially useful for women with dense breasts. However, MBI is not as widely available as other screening methods.
While these additional tests may be useful in women with dense breasts, they come with their own risks. They may detect benign abnormalities, leading to unnecessary biopsies and treatments, as well as expose patients to additional radiation. In terms of cost, tests like Breast MRIs may not be covered by all insurance providers unless the patient is at a very high risk of breast cancer. Dense breasts alone do not constitute a very high risk.
Lastly, while these tests may pick up more breast cancers than a regular mammogram, they have not been demonstrated to reduce the risk of dying from breast cancer.
Questions to Ask Your Doctor
- What is my breast density?
- How has my breast density changed over the years?
- Does my breast density put me at a higher risk for breast cancer?
- Is the rate of change of my breast density concerning for an elevated breast cancer risk?
- How frequently should I get mammograms?
- Which mammogram centers offer 3D mammograms?
- Should I get additional testing, such as breast MRIs, based on my cancer risk?
- What are the benefits and risks of getting additional testing?