Breast Density Q&A with Dr. Chan
Breast density is a topic that is covered in mystery. Maybe you’ve received your mammogram report, and you are trying to understand what it means. Well, that’s why we sat down with Dr. Ariane Chan, a researcher that works with breast density issues every day through her work at Volpara Health, a company that uses artificial intelligence to build products that assess breast density taken with mammograms.
Interview with Ariane Chan, PhD
Global Lead, Clinical Research & Medical Affairs @ Volpara Health
Q: What is breast density and how is it determined?
Dr. Chan: Breasts are made up of three tissues: glandular tissue, fibrous tissue and fatty tissue. Glandular tissue produces milk and allows breastfeeding, this is surrounded by fibrous and fatty tissue that support the breast and give it its shape.
Breast density is a measure of the relative amounts of these tissues. If there is more of the fibrous and glandular tissue (often grouped together as “fibroglandular tissue” or “dense tissue”), then the breasts are considered to be more dense. If there is more fatty tissue, the breasts are considered to be less dense.
Breast density isn’t something that can be seen or felt by touching the breast, but it can be determined by a mammogram, a type of imaging used for breast cancer screening that uses x-rays. On a mammogram, fibroglandular tissue appears whiter, and fatty tissue appears darker, and this allows clinicians and researchers to assess breast density.
There are three common methods to assess this:
One way is by a radiologist looking at the x-ray and deciding how much white (fibroglandular) tissue there is in the breast, rating them from categories a - d, like in the image above. Women with breasts in the c or d category are considered to have “dense” breasts.
The second way is to use software that can “read” the density. This can produce a more consistent assessment of breast tissue based on complex algorithms that try to mimic the four categories used by radiologists.
The third way is to use software to measure the amount of dense tissue in the breast. If you think about BMI, which is a measure of body fat based on a person's height and weight, patients are often grouped into Underweight, Normal, Overweight or Obese BMI categories, even though BMI can be calculated as an actual number. The first method would be like looking at someone and guessing which BMI category you thought they would fall into. With these newer methods using software, the measurements are more personalized and would be more like measuring a person's actual height and weight using a tape measure and scales, to calculate the true BMI number. Because breasts are 3-dimensional, some of these methods are volume-based and take the breast size into account to calculate the overall density. There are some really interesting things happening with technology to better understand density.
It is normal and expected for the pattern and brightness of breast tissue on a mammogram to vary a lot as every woman's mammogram is unique, in a similar way to how fingerprints are unique.
The picture above gives you a general idea of what an a/b/c/d category looks like. The actual mammogram images below show how more personalized measurements of dense tissue (on a scale of 0-100%) can further separate out women who would normally fall in the same category, in this case two women in the “d” category. Notice how challenging it can be to find tumors (pictured here as a star) behind the dense tissue, particularly when it is more dense? This is why reliable measures of breast density are so important for helping clinicians make decisions when it comes to screening more effectively.
Image courtesy of Volpara Health, showing their personalized volume-based measures of breast density. VBD% stands for “Volumetric Breast Density percent”, a measurement of the proportion of dense tissue in the breast, on a scale of 0-100%. The two images are mammograms from different women, both judged as being in the extremely dense or “d” category, but the VBD% suggests measurable differences in the breast density between the women. A star, to represent a cancer, is shown on each mammogram, and shows how dense tissue in the breast can more easily hide cancers.
Q: Does breast density change throughout a woman’s life?
Dr. Chan: The short answer is “yes”, but between individuals it can vary based on different factors. Breast tissue tends to decrease with age due to the natural process of “lobular involution,” where the glandular tissue gradually disappears (and is eventually replaced with fat). And in some women there is a more noticeable decrease during the transition to menopause.
Although breast density can be something you can inherit, lifestyle and behavioural factors can also impact a woman’s breast density. Some research, for example, has found that weight/BMI changes, physical activity, diet, and certain hormone replacement therapies or breast cancer risk-reducing medications (e.g. tamoxifen), can cause measurable density changes within relatively short time frames of several months to 1-2 years.
While these impacts may be less obvious, other factors, such as the age at which women first got their period, started menopause, or had their first child, how many children they had and how long they breastfed for, family history and alcohol consumption, have all been shown to influence breast density.
(Our Know Your Lemons App risk quiz helps you understand those risks too.)
Q: So does your risk increase if you have dense breasts?
Dr. Chan: Yes, for two reasons: one, it can increase the risk of developing breast cancer; and two, it decreases the ability to detect breast cancer through mammography screening. This is because tumors or calcifications show up white, just like dense tissue does, making it harder for radiologists to see them on the mammogram.
For example, for women with the least dense breasts, around 9 out of 10 breast cancers are detected with mammography. But for women with “extremely dense” breasts, the detection rate can drop to around 6 out of 10 breast cancers. Knowing if one has a high level of breast density can mean that supplemental imaging such as ultrasound or MRI, in addition to mammography, can be used to improve cancer detection for the goal of early detection. Because when found early, survival rates are incredibly high.
Cancers detected outside of screening are often larger and are associated with lower survival so having the right screening plan is key to managing risk. The risk of developing breast cancer is 4 to 6 times higher in women with extremely dense breasts, compared to women with almost entirely fatty breasts, or around 2-fold higher compared to women with ‘average’ breast density. This 2-fold increased risk is similar to the risk associated with having a family history of breast cancer in a first degree relative (e.g. a parent, child, sister or brother).
But, these sorts of statistics don’t tell the full story, because many of the factors that can influence breast density are themselves also risk factors for breast cancer (called ‘confounders’). Age and BMI are particularly important confounders - both are risk factors for breast cancer, but younger women or women with lower BMI, for example, tend to have denser breasts. For an individual woman, whether breast density increases or decreases her risk seems to be heavily tied into whether her breast density is higher or lower than the predicted density for her particular age and Body Mass Index (BMI).
These confounders are also important when trying to understand the impact of breast density on breast cancer risk for different ethnic and racial populations. African American women, for example, tend to be more overweight or obese on average, compared to non-Hispanic white women, but if you account for factors like age and BMI, then African American women are more likely to have denser breasts. Researchers are still trying to understand whether these breast density differences contribute to the fact that African American women tend to be diagnosed at younger ages and have more aggressive cancers compared to white women.
Research has also shown that changes in density can influence breast cancer risk. For example, women who experience decreases in breast density after taking breast cancer risk-reducing medications (e.g. tamoxifen) are more likely to have their breast cancer risk lowered. There is also evidence that increases in breast density in response to hormone replacement therapies can increase breast cancer risk.
Q: I have dense breasts. How can I best stay on top of my breast health?
Dr. Chan: There are so many conflicting opinions about what women should or shouldn’t be told about their breast density, or what they should or shouldn’t do if they have denser breasts. Based on my own experiences, I’ve highlighted five key things to keep in mind to help women become more breast aware:
Be your own advocate to find out if you have dense breasts
For some women getting mammography screening, radiologists don’t have to tell them what their breast density is, and I am a strong believer that women have the right to know so that they can make the best decisions for their own breast health. If they don’t tell you, ask!
Understand the limitations of mammography for women with denser breasts
Mammography screening doesn't work equally well for all women, especially those with denser breasts. It’s important that women with dense breasts still attend regular screening but they should also understand that their own breast density can make it harder for radiologists to find cancers in their breast.
Understand the pros and cons of supplemental screening options
For women with denser breasts, there are other imaging options that can be used in addition to mammography to increase cancer detection rates, but women need to weigh up their benefits and limitations based on their own personal preferences and what’s important to them. There may be, for example, additional out-of-pocket costs for supplemental imaging and such imaging can increase false-positives, leading to unnecessary call backs or biopsies. Finding cancers earlier may mean less aggressive surgeries and/or drugs, but research is still ongoing to try and understand whether supplemental imaging reduces the rates of women dying from breast cancer.
Be aware of your breast cancer risk
Breast density is one of many risk factors for breast cancer that women should be aware of, and it’s important to remember that just because a woman has dense breasts doesn’t mean she is at increased risk for breast cancer. Some risk factors are also modifiable, meaning that they can be changed, and so learning about the different risk factors can help women make lifestyle and behavioral changes that reduce their breast cancer risk.
Women don’t need to wait until they start mammography screening to understand their breast cancer risk. The free Know Your Lemons® app provides a risk calculator that includes the question of breast density. And once women start mammography screening, they can reassess their breast cancer risk including breast density. It is especially important for women from certain ethnic or racial groups to understand their risk factors, as they may be more likely to have denser breasts and tend to be diagnosed with breast cancer at younger ages, for example African American and Asian women.
Not all high-risk women go on to develop breast cancer, and some low-risk women will develop breast cancer. However, understanding your own risk can help you make decisions about screening or prevention options, such as how often to get screening, whether to get supplemental imaging, whether to get genetic testing, or whether to take breast cancer risk-reducing medications.
Understand that, like breast density, breast cancer risk can change.
A woman’s breast cancer risk can change from one year to the next, especially if there are more notable changes in risk factors (e.g. if a new family member develops breast or ovarian cancer). Keeping track of your family history and other risk factors and updating your doctor of any changes is important.
Thank you Dr. Chan for this information and taking the time to help us understand more about breast density and what we can do with that knowledge when it comes to early detection.
Dr. Chan: It’s my pleasure!
For further information on breast density, visit Volpara’s breast density website or speak to your doctor.
Assess your individual risk with our new Know Your Lemons app. It’s free and fun and teaches about the different breast tests available, as well as alternative screening options if you have dense breasts.
This blog post was originally published on 15 October 2021.