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Fibroglandular Density - What Breast Density Actually Means

Over the last several years, breast cancer screening standards have evolved to improve detection rates for women with high fibroglandular density.

From what fibroglandular tissue is and how it’s determined to why it impacts your mammogram and how a second opinion can help reduce your risk of misdiagnosis - here’s your guide to understanding what breast density means for you.

What is Fibroglandular Tissue?

Breasts are made up of different types of tissues. They can be split up into three categories: fatty tissue, fibrous tissue, and glandular tissue.

  1. Glandular tissue - Includes the breast lobes and breast ducts that produce and carry milk to the nipple.

  2. Fibrous tissue - Acts as supportive and connective tissue.

  3. Fatty tissue - Give breasts their shape and size; fills in the space between glandular and fibrous tissue.

All non-fatty tissue is considered fibroglandular tissue.

What is Fibroglandular Density?

fibroglandular_density_levels.png Photo source: Cassling.com

Breast density refers to the amount of fibroglandular tissue (fibrous and glandular tissues) that makes up a woman’s breast. A dense breast will have more fibrous and/or glandular tissue, with less fatty tissue.

There are four levels (or classes) of breast fibroglandular density: fatty, scattered fibroglandular density, heterogeneously dense, extremely dense.

Between 40 and 50 percent of women aged 40-74 in the U.S. have dense breasts.

In terms of breast cancer screening and detection, fibroglandular tissue (breast density) has two major areas of impact:

  • It makes breast cancer screening with mammography more difficult.
  • It can increase your risk for breast cancer.

While the reason breast density increases risk is not fully understood, studies have consistently found that women with high fibroglandular density have around a four to five times higher risk of developing breast cancer compared to women with low breast density.

It’s important to remember, however, that there is currently no evidence supporting any link between fibroglandular density and response to treatment or survival rates.


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How Does Breast Density Affect Your Mammogram?

Fibroglandular density affects the way a breast appears on a mammogram - dense breast tissue will appear white, while fatty breast tissue will look black.

This presents a huge diagnostic challenge because cancer cells also appear white on a mammogram. While high to scattered fibroglandular densities create the most distortion; any degree of fibroglandular density impacts the level of detail captured on a mammogram.

To help reduce the risk of missed tumors and masses, additional imaging tests, such as breast ultrasound, breast MRI, and 3D mammography (tomosynthesis) are recommended for patients with dense breasts. With a stronger ability to differentiate between tissues, these tests allow the radiologist to get a more clear picture. In fact, research found that ultrasound tomography can detect breast cancer in dense breasts with up to 90 percent accuracy, compared to only 50 percent using mammography.

But while advanced imaging is certainly capable of capturing more information, it requires a much higher level of expertise from the interpreting radiologist.

In general, an imaging test, whether it be a mammogram or breast ultrasound, is only a piece of the screening process. Detection and evaluation of an abnormality depends greatly on the ability of the radiologist. It takes a high level of skill and expertise to detect earlier and more subtle manifestations of the disease.

It’s estimated that over 90,000 women get a breast cancer misdiagnosis.

Accuracy is improved when mammograms and other scans are interpreted by dedicated subspecialists (radiologists specializing in breast imaging). Especially for patients with high fibroglandular tissue, a second opinion by a subspecialist can help reduce the risk of missed abnormalities.

But as of July 2019, only 38 states have breast density laws in place that require some level of breast density notification after a mammogram. And some of those laws only require general notification about breast density - without requirement for a patient be informed about her own breast density.

While the FDA is taking steps to standardize these laws, it may take some time before we see nationwide breast density notification laws take effect. Fortunately, an increase in awareness on breast screening is empowering patients with the information they need to make important health decisions.

Why Get a Breast Imaging Second Opinion

A second opinion from a breast imaging subspecialist is valuable for both patients with and without a breast cancer diagnosis.

For those without a diagnosis, it can offer peace of mind and confirmation that nothing was missed. Or, it could potentially prevent a missed cancer diagnosis. For patients with a breast cancer diagnosis, it can help ensure the cancer was accurately staged and confirm the best course of treatment is planned. It can also help prevent false positives.

51% of breast cancer second opinions result in a changed diagnosis.

Even for women with little to no dense breast tissue, mammography is not always accurate. Data from the Breast Cancer Surveillance Consortium found that conventional mammography accurately identifies about 87 percent of women who truly have breast cancer. That means the other 13% of women are misdiagnosed with either a false positive or a false negative.

In addition to negative psychological effects, a false positive can lead to unnecessary, costly testing or harmful procedures, such as biopsy. A false negative can have huge consequences on a patient’s chance of survival. A second opinion can help decrease the risk of misdiagnosis.

How Is Breast Density Determined?

Breast density can only be determined through screening. Breast size is not at all an indication, and you cannot gauge the density of breasts by touch and feel.

Dense breasts are very common in women and are completely normal. What causes fibroglandular density is not completely clear to doctors; however, there are few factors associated with dense breasts:

Age - Breast tissue tends to become less dense with age. However, this is not always the case. Some women will have dense breast regardless of age.

Body mass index - Women with less body fat and a lower body mass index are more likely to have more dense breast tissue compared with women who have a higher body mass index.

Hormone intake - Women who take hormone therapy for menopause are more likely to have dense breasts.

By informing women of their breast density and providing education on what that actually means - physicians can help personalize a woman's health care. Breast density and breast cancer risk are unique to each and every woman. Other factors, like family history, also play a role. The followup test(s) suggested for one woman with dense breast may differ vastly from that of another woman with high fibroglandular tissue.

If you have questions or concerns about the density of your breast, or in regards to the best screening for your particular body, be sure to consult a healthcare provider.

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In this article...

What is Fibroglandular Tissue? What is Fibroglandular Density? How Does Breast Density Affect Your Mammogram? Why Get a Breast Imaging Second Opinion How Is Breast Density Determined?

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