Do you have dense breasts?

Do You Have Dense Breasts?

I’ve known since I was 40 that I have dense breasts, but I did not understand the risks. Last night I learned that I have the highest breast density, category D. I also learned that those of us with extremely dense breasts have a greater risk of developing breast cancer than someone with a family history of breast cancer. That got my attention.

Dense breasts are not a symptoms of perimenopause, but all women in their 40s should be paying attention to their breasts and understand their risk factors. This could save your life, particularly if you have dense breasts.

Dense Breasts Canada

I was speaking with Jennie Dale who is a co-founder of Dense Breasts Canada, a non-profit organization committed to raising awareness about the risks associated with dense breasts and advocating for optimal breast cancer screening.

What Jennie told me was alarming.

What follows is information from Dense Breasts Canada that should be discussed with your medical provider.

All Women Should Be Screened Starting At 40

I was shocked to learn that 85% of all breast cancer occurs in women with no family history of breast cancer. In fact, the most significant risk factors for breast cancer are being a woman and growing older.

A Canadian study showed that women in their 40s who have mammograms are 44% less likely to die from breast cancer than those who don’t.

That’s why all women should be screened for breast cancer starting at age 40. And women with dense breasts should have supplemental screening. Sadly, neither of these recommendations are part of the current Canadian breast cancer screening guidelines.

I know. WTF? More on this later.

The only way to determine breast density is with a mammogram
The only way to determine breast density is with a mammogram

What Is Breast Density?

Every woman’s breast composition is unique. Every woman has fat, glands, and fibrous tissue in her breasts, but the proportions of each vary from woman to woman. Breasts that have more glands and fibrous tissue than fat are called dense breasts.

Dense breasts are normal and common. More than 40% of women, between the ages of 40-74 have dense breasts.

There are 4 categories of breast density. The only way to determine breast density is with a mammogram.

Breast Density Categories

Radiologists divide breast density into 4 categories A to D, using the Breast Imaging Reporting and Data system, or BIRADS. Some provinces describe the categories in words.

Categories C and D are considered dense breasts.

Category A | Almost Entirely Fatty

The breasts have little fibrous and glandular tissue and are mostly fat. A mammogram would likely detect an abnormality.

Category B | Scattered Areas of Fibroglandular Density

The breasts have scattered areas of fibrous and glandular tissue, but also quite a bit of fat.

Category C | Heterogeneously Dense

The breasts have consistently distributed areas of fibrous and glandular tissue, making it hard for small masses to be detected by mammogram.

Category D | Extremely Dense Breasts

The breasts have a lot of fibrous and glandular tissue, making it even harder for a cancerous tumor to be detected by mammogram.

Breast Density Categories

What Factors Affect Breast Density?

AGE: Dense breasts are more common in younger women.  As women get older, their breasts usually become less dense, but not always.

  • 56% of women in their 40s have dense breasts.
  • 37% of women in their 50s have dense breasts.
  • 27% of women in their 60s have dense breasts.

MENOPAUSE: Density usually decreases after menopause, but not always.

ETHNICITY: A greater percentage of Asian women have dense breasts.

HEREDITY: Breast density can be inherited.

HRT: Density increases in women on hormone replacement therapy.

BREAST SIZE: Smaller breast size is related to higher density.

PREGNANCY/ BREASTFEEDING: Breasts become denser during this time.

WEIGHT: A higher BMI is inversely related to density.

AROMATASE INHIBITORS AND TAMOXIFEN: The use of these cancer drugs decreases density.

Why Breast Density Matters


Radiologists say that looking for cancer in a dense breast is like looking for a snowball in a snowstorm. A small cancer, easily seen in a fatty breast, can be hidden in normal dense breast tissue.

Dense breasts increase the risk that cancer can be missed on a mammogram and increase the risk of getting breast cancer. Women in Category D have a 4-6 times higher risk of developing breast cancer than women with fatty breasts.

Since both cancer and dense tissue appear white on a mammogram, supplemental screening with an ultrasound is recommended by the Canadian Association of Radiologists and the Canadian Society of Breast Imaging.

Supplemental screening for Dense breast tissue

If you have dense breasts, speak to your medical provider about supplemental screening with a breast ultrasound. A ‘normal’ mammogram may not be accurate. Dense breast tissue can mask cancer. Ultrasounds can find additional cancers that a mammogram may have missed.

It is important to note that ultrasound is a sensitive test and can sometimes result in false positives, where the test finds an abnormality that is not cancer. This can be scary. My personal choice is that I would rather risk being scared than risk having a cancer grow undetected. And that is what is important; it should be your choice.

Breast Imaging Challenges

Mammograms find 81-93% of cancers in women with fatty breasts, but miss up to 43% in women with the densest breasts.

Risk of an interval cancer is 18 times higher in women with dense breasts. An interval cancer is a cancer discovered between screenings, usually as a lump. These cancers have a worse prognosis than those found as a screen-detected cancer.

It’s important for women with dense breasts to know their breast density because if they’re told that their mammogram is negative, it can give them a false sense of security.

Do You Know Your Breast Density?

Early detection of breast cancer should not depend on your postal code.
Early detection shouldn’t depend on your postal code








Currently all women having a screening mammogram in six provinces (BC, AB, MB, NS, PEI, NB) are directly informed of their breast density in the mammogram results letter mailed to them. Women in five jurisdictions (NL, NWT, YT, ON, SK) are only told if they have the highest category of density. All but YT will begin telling all women later in 2023 thanks to the advocacy efforts of Dense Breasts Canada.

There are only 6 jurisdictions in Canada where you will be asked to return for an annual mammogram if you have category D breast density. This is problematic because there are fewer interval cancers in provinces where women with dense breasts have annual mammograms.

Check out to understand the screening guidelines in your province. Pissed off that early breast cancer detection in Canada may depend on your postal code? This site also provides a customized letter you can download and send to your Provincial Health Minister.

Breast Density Facts

  • Their is a greater risk of getting breast cancer when breasts are dense.
  • Having dense breasts is a more prevalent risk factor than a family history.
  • Their is a greater likelihood of a cancer being missed on a mammogram when breasts are dense because of the camouflage effect: dense tissue and cancer both appear white on a mammogram.
  • Up to 43% of cancers are missed in women with the highest density.
  • Ultrasound can find cancers missed on a mammogram when breasts are dense, even if 3D mammogram is used.

Breast Cancer Screening Guidelines Are A Problem

According to, the guidelines for Canadian breast cancer screening were made by the Canadian Task Force on Preventive Health Care (CTF). While the panel included experts in methodology, it did not include any experts in breast cancer screening.

The panel included a psychologist, an occupational therapist, and a nephrologist (kidney specialist), family doctors, nurses, a chiropractor, and an emergency room doctor. The guidelines ignored the input of experts in breast cancer diagnosis and treatment.

The diagram below shows the difference in recommendations as provided by Dense Breasts Canada:

Screening Recommendations Comparison Chart Courtesy of Dense Breasts Canada

Supplemental Screening And Breast Cancer Risk

The Canadian Task Force on Preventive Health Care says there’s insufficient evidence to recommend supplementary screening for women with dense breasts. This statement is a result of the Task Force’s insistence on using only Randomized Control Trials (RCT) to support their guidelines.

An RCT of screening ultrasound is underway in Japan, but it will take at least 7-10 years before it can prove mortality reduction. This RCT is already showing that they’re finding more early cancers in women having both mammography and ultrasound, and that those women have fewer interval cancers.

There is observational data from multiple studies starting in 1995 showing that ultrasound finds an additional 3-7 cancers per thousand women. Finding these cancers earlier will allow for less aggressive treatment and reduce mortality.

Breast Density To Do List

  • Find out your breast density.
  • Consider requesting an annual mammogram. This lowers the risk of interval cancer.
  • Consider requesting a screening breast ultrasound, in addition to your mammogram.
  • Continue having mammograms because they can detect cancer not visible on an ultrasound.
  • Perform regular self-exams, ideally every month.
  • If you’re still menstruating, do the exam just after your period.
  • If you notice any change, see your health care provider. Even if you just had a negative mammogram.
  • Consider modifying your lifestyle factors to decrease cancer risk, such as maintaining a healthy weight, doing moderate exercise, and decreasing alcohol intake.
  • If you are taking combined estrogen and progestin therapy, review the risks and benefits of this therapy in the context of your breast density with a qualified medical provider.

The Hero Bit

As always, discuss the above information with your medical provider. Getting a baseline for your health, and particularly your breasts is important. Knowing your breast density is very important. You may need to self-advocate if you’re not in a jurisdiction that recommends annual breast screening starting at age 40, or if you want supplemental ultrasound screening for dense breasts. has scripts to help you ask for the care you need.

Not sure how to perform a self-exam? Dr. Paula Gordon, who is the medical advisor at Dense Breasts Canada, recommends this video to learn how to properly do a breast self exam.


The intent of this information is to provide the reader with knowledge to support more efficient and effective communication with their medical providers. This information is not intended as medical advice.