New FDA Mammogram Reporting Regulations – Breast Density

As many people have probably seen in the news, the Federal Drug Administration (FDA) recently updated its mammography regulations which will go into effect on September 10, 2024. Specifically, the regulations impact the reporting on breast density classification. All women fall into one of the four following categories:

• Almost Entirely Fatty
• Scattered Areas of Fibroglandular Density
• Heterogeneously Dense
• Extremely Dense

The FDA issued initial regulations in the Mammography Quality Standards Act (MQSA) of 1992 that laid out how mammograms needed to be performed, what information needed to be captured, and what information needed to be shared with patients. Currently, mammography is the main breast cancer screening tool. The MQSA had some pretty significant impacts like a marked decrease in the number of facilities that provided sub-par mammography services to women. It has also probably played some role in helping to increase the number of breast cancers detected. While some of that is owing to technological improvements, standards have probably helped. This new amendment to the regulations reflects years of observational data and scientific investigation into the impact that breast density has on cancer risk.

The amendment means that radiologists (the doctors who perform and read the mammograms) must provide language in their report for patients and doctors. The patient summary will be a lay description of their breast density in terms they can understand. The doctor summary will go to whichever doctor ordered the mammogram (e.g. ob/gyn, breast surgeon, etc.) and will provide the categorization of the breast density.

Patients will receive one of the following notifications:

Physicians will receive a notification that is consistent with the breast density categories I provided at the beginning of this post.

You can see that as a patient, you are not going to be told necessarily which category of breast density you fall into, but you can know that if you receive the Dense Notification you are probably in Category C or D . Plus, you can use this to start a conversation with your doctor.

What is breast density?

What does it mean to have non-dense versus dense breasts? I know that was a question that I had! I understood there had to be differences in density in order for a mammogram to show anything, but I didn’t actually know what it meant for you to have dense or non-dense breasts. Let’s look at the Category A first – entirely fatty. This does not mean that you are fat, it has more to do with the description of the types of cells that make up your breast. In a breast, there are four main types of tissue – glandular, fibrous and fatty.

Glandular tissue is similar to the types of tissue that are found in the lining of organs. In the breast, this includes your lobules (the organs that produce breast milk) and breast ducts (the pathways that carry breast milk). Fibrous tissue is connective tissue that helps to hold together the structures of the breasts like ligaments. Many times these two categories are combined to be referred to collectively has “fibroglandular” tissue. Fatty tissue is exactly that – fat cells. Thinner women might have less fat cells in their breasts, but not necessarily. I’ve cited some sources at the end of this post if you want to read more about breast tissue and structure from the Cancer.gov and Memorial Sloan Kettering.

Women with denser breasts will have a higher proportion of the fibroglandular tissue compared to fatty tissues. Fibroglandular tissue is more dense than fatty tissues. This means that on imaging, the fibroglandular tissue will look grayer compared to the fat tissue. Therefore, when you have dense breasts, your mammogram will have more grayish, white-ish spots on it than someone with less dense breasts. And generally, tumors will look gray/white as well. So if you have normal tissue that is the same color as the tumor, it might be hard to see contrast between the two different tissues. You can see this when you look at the picture I included from DenseBreast-info.org above.

Who has dense breasts?

According to a study of breast density prevalence from 2014 by B.L. Sprague, et al, approximately 43% of women between the ages of 40 to 74 years of age had heterogeneously or extremely dense breasts (Category C and D). They also found that breast density was inversely related to age, so, as you age, your breasts tend to get less dense. This obviously does not cover women who are younger than 40, who probably have an even higher proportion of fibroglandular tissue.

Interestingly, there is evidence to suggest that the density of your breasts can change over time for a lot of different reasons. For instance, in a paper by L. A. Prebil, et al. they wanted to examine the impact that age of first pregnancy, breastfeeding, number of pregnancies and other characteristics had on fibroglandular volume as women aged. While the point of the paper was not to make any sort of assessment on breast cancer risk, they were motivated to study the topic because of the association of breast density to breast cancer risk. What they found was that earlier age of pregnancy, more pregnancies and less months of breastfeeding resulted in less dense breasts. Women who were older at their first pregnancy, had less pregnancies or who breast fed longer tended to have higher amounts of fibroglandular tissue.

There have been additional epidemiological studies that have shown women being treated with Metformin for diabetes have a lower risk of breast cancer compared to their “normal” matched women. Scientists are exploring what impact Metformin might have, but there is some evidence to suggest it lowers breast density. There might also be an impact of the type of diet (e.g. high in refined sugar, higher in carbohydrates, etc.) on breast density as well. There are a lot of studies out there – probably enough for several separate blog posts – and I’m no expert. The main points is that a lot of women have dense breasts and there are a lot of things that can affect your breast density over the course of your life.

Why does breast density matter?

Impact on imaging

I think this is one of the often cited risks that dense breasts have for breast cancer risk and is evident in the image I shared above. It actually has nothing to do with your actual risk of developing breast cancer, but more to do with anyone being able to see it on imaging when it’s early and small. This makes a lot of sense – if there is stuff that obscures your view, it’s going to be hard to see a tumor – especially a small one!

I know a lot of women hate mammograms because they have to squeeze your breast between two hard, plastic plates while you stand “hugging” a machine. The main reason your breast has to be smushed like that is partly because you won’t be able to achieve the type of resolution you want or get as clear of images without “flattening” it out and making the tissue thinner. So dense breasts mean you have more, tougher structures that can’t be flattened as nicely either.

For these reasons, knowing that you have denser breasts will allow you to have a conversation with your doctor where you might ask “Are there any other imaging tests I can do?” The answer to that is, yes. MRIs are actually the best way to image, but the tests are long, expensive and not as readily available. You might also be able to request an ultrasound to accompany your mammogram. A third common option is tomosynthesis, also referred to as a 3-Dimensional mammogram. But again, no imaging technique is absolutely perfect.

This is actually where Artificial Intelligence (AI) use – specifically neural networks – becomes applicable in imaging. Many of you have probably seen the headlines recently about AI being used to catch breast cancer that physicians “miss.” As many faults as I can find with medical care and its quality today, I consider the headline to be a bit disingenuous to radiologists. An image is presently never going to 100% confirm your diagnosis – only a biopsy will do that. But AI could assist radiologists in taking a closer second look or maybe doing a biopsy.

Implications for breast cancer risk

For many years, people have seen in epidemiological data that there is a correlation between breast density and cancer risk that couldn’t be explained by difficulty in imaging alone. Unfortunately, they weren’t able to explain scientifically why exactly that was the case. More scientists today are in agreement that breast density definitely affects your cancer risk, but there are still a lot of people who just do not think the data is there to support that. This is evident in the fact that some medical professionals disagreed with the FDA issuing this amendment to the regulation.

In November of 2022, a group of scientists released a paper where they looked very closely at breast density across a spectrum of women with varying densities. One of the important aspects of their study was that they not only imaged the breasts, but they studied the microenvironment breast tissue. They were able to show scientific proof that dense breasts are, in fact, different from non-dense breasts. The study completed by P. Lundberg, et al involved performing MRIs on post-menopausal women while also completing a microdialysis (separating different types of very small molecules). By completing these two different analyses, they were able to show that the tissue environment in denser breasts actually possessed pro-tumorigenic properties.

To be clear, in their paper they specifically say that they cannot draw a causal relationship between breast density and cancer development. They will take their findings from this paper and conduct more studies to try and prove a causal relationship, which they feel their initial findings strongly support. Again, this doesn’t mean that if you have dense breasts you will definitely get breast cancer. But it could mean that denser breast tissue has more in common with breast tumors and, therefore, mean that if you have a higher proportion of that type of tissue you’d be at increased risk.

Helping to make personal decisions

All of this means that they are trying to give the individual more information so they can make better decisions for themselves. Medicine can be criticized heavily for being paternalistic – why give people information about things they don’t understand or have expertise in? But if no one shares this information with the individual, they don’t even have a chance to ask more questions. Or go to talk to a different doctor who might have a totally different opinion!

One of the things you hear a lot about in the breast cancer community, and the cancer community in general, is that you have to be your own advocate. And the only way you can truly advocate for yourself is if you have information. Not to mention that when you go to get a mammogram, they are taking images of your body! That is your property, your information, your data! You can choose to do nothing with it, look at it, ignore it, ask questions about it, etc. But the whole point is that you get to make that decision.

What impact does this have for me personally?

Personally, I think this is a net-positive change for women. You probably could have guessed that from the fact I even wrote this post! It is always net beneficial to give people access to their own data and it’s even more important to try to put it in simple language that people will generally understand.

Unfortunately, I don’t think this is going to have much of a direct impact for my age group. For me and the other thousands of women like me on an annual basis who receive a breast cancer diagnosis before the age of 40, we were never eligible for breast cancer screening anyways! How would any one have ever had the opportunity to tell me I had dense breasts. And even still, it is pretty much accepted that women in my age group have dense breasts because we are young.

Some young women who have been diagnosed with breast cancer get angry about the lack of screening in younger women. There is no doubt in my mind that we need better screening tools, but lowering the age for mammography is definitely not the solution. Mammography requires the use of radiation to get the images and having regular radiation exposure starting in your 20s is going to give you breast cancer rather than preventing it.

It’s possible that an initial mammography “assessment” for young women could be helpful. The purpose would not be looking for breast cancer, but to gauge the relative proportion of dense tissue in younger women. As we learn more about what affects breast density, this might help to counsel women on changes they can make to lower it. But I also appreciate the fact that doing that kind of test could have unintended consequences like false-positives or unequivocal results that lead to a bunch of unnecessary and intrusive testing or unnecessary worry.

Overall I am supportive of this change and any change that gives people better access to their own health information!

Additional Citations

Dense Breasts: Answers to Commonly Asked Questions, https://www.cancer.gov/types/breast/breast-changes/dense-breasts

Anatomy of the Breast, https://www.mskcc.org/cancer-care/types/breast/anatomy-breast

Sprague BL, Gangnon RE, Burt V, Trentham-Dietz A, Hampton JM, Wellman RD, Kerlikowske K, Miglioretti DL. Prevalence of mammographically dense breasts in the United States. J Natl Cancer Inst. 2014 Sep 12;106(10):dju255. doi: 10.1093/jnci/dju255. PMID: 25217577; PMCID: PMC4200066.

Prebil LA, Ereman RR, Powell MJ, Jamshidian F, Kerlikowske K, Shepherd JA, Hurlbert MS, Benz CC. First pregnancy events and future breast density: modification by age at first pregnancy and specific VEGF and IGF1R gene variants. Cancer Causes Control. 2014 Jul;25(7):859-68. doi: 10.1007/s10552-014-0386-2. Epub 2014 May 7. PMID: 24801045; PMCID: PMC4048469.

Lundberg, P., Forsgren, M.F., Tellman, J. et al. Breast density is strongly associated with multiparametric magnetic resonance imaging biomarkers and pro-tumorigenic proteins in situ. Br J Cancer 127, 2025–2033 (2022). https://doi.org/10.1038/s41416-022-01976-3