What Is Breast Density?

Each woman’s breast composition is unique. Every woman has fat, glands and fibrous tissue in her breasts, but the proportions vary woman to woman.

What are dense breasts? How common are they?

Each woman’s breast composition is unique. Every woman has fat, glands and fibrous tissue in her breasts, but the proportions vary woman to woman.

Breasts that have more than 50% glands and fibrous tissue are called dense breasts. 

Dense breasts are common. For women aged 40-74 years, 43% have dense breasts. Breasts usually become less dense and more fatty with age:

  • 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.

It is normal to have dense breasts, but women need to know if they have dense breasts so that they can understand the implications.

How is my breast density assessed?

Your breast density is determined by the radiologist reviewing your mammogram. Some provinces now use software to measure a woman’s level of density on a mammogram. Breast density is NOT determined by the size or firmness of your breasts. You cannot tell density by look or feel and neither can your family doctor/nurse practitioner.

Dense breasts are not the same as lumpy breasts.

What categories are used to describe breast density in Canada?

Breast density is described using 4 categories but the categories vary by province.

Percentages (0-100%), letters (A,B,C,D) or words can be used.

UNDER 25% dense tissue | Category A | Almost entirely fatty
The breasts have little fibrous and glandular tissue and are mostly fat. A mammogram would likely detect an abnormality.

25%-50% dense tissue | Category B | Scattered areas of fibroglandular density
The breasts have scattered areas of fibrous and glandular tissue, but also quite a bit of fat.

51-74% dense tissue | 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.

75% and above dense tissue | 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.

** ABOVE 50% / CATEGORY C and D ARE CONSIDERED DENSE BREASTS.
Dense breast tissue may obscure small tumors and make a mammogram less accurate.

How many women have "fatty' vs "dense" breasts?

Four categories are used to describe the range of breast density.

  • 10% of women have the lowest category of density known as ‘Fatty’ breasts 
  • 40% have ‘Scattered areas’ of density.
  • 10% of women fall in the highest category ‘Extremely Dense.’ (considered dense breasts)
  • 40% of women fall in the category Heterogeneously dense breasts (considered dense breast).

The higher the density, the higher the risk of breast cancer and that a tumour will be missed.

Mammogram showing breats density

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 HRT.

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.

What if I don't have dense breasts?

Studies show that regular mammograms reduce mortality. Even if you do not have dense breasts, other factors may still place you at increased risk. Talk to your doctor/nurse practitioner and discuss your history. Women considered to be at high risk will likely be sent for an MRI, as well as a mammogram. Screening saves lives.

Young Caucasian adult woman examining her breast for lumps or signs of breast cancer
why breast density matters

Why Breast Density Matters?

Dense breasts make it harder for doctors to spot cancer because both cancer and dense breast tissue appear white on mammograms. A camouflage effect is created.

How does my breast density affect my mammogram?

Dense breasts make it harder for doctors to spot cancer because BOTH CANCER AND DENSE TISSUE APPEAR WHITE on mammograms. A camouflage effect is created.  Fatty tissue allows greater x-ray penetration and shows as black or dark grey on a mammogram; the contrast makes cancer easier to detect in fatty breasts. Mammograms are 98% accurate in women with fatty breasts, but only 50% accurate in women with the densest breasts (Extremely Dense Breasts/ Category D, >75% dense tissue). 

Kolb, T., Lichy, J., & Newhouse, J. (2002). Comparison of the performance of screening mammography, physical examination, and breast US and evaluation of factors that influence them: an analysis of 27,825 patient evaluations. Radiology. (225):165–17. View Study 

WHAT ABOUT 3D MAMMOGRAM (TOMOSYNTHESIS)?

Tomosynthesis (3D mammogram) is available in a few provinces as a screening tool, but for now is mostly used as a diagnostic tool. It increases the detection of invasive cancer by an additional 1-2 cancers per 1000 women. However, its effectiveness declines as the density increases. Tomosynthesis does not detect as many cancers in women with the densest breasts (women with over 75% dense tissue/ Extremely Dense Breasts).

Supplementary ultrasound detects more cancers in dense breasts than Tomosynthesis. The evidence for the past 40 years shows that mammography is not enough for women with dense breasts.

How does breast density affect my cancer risk?

The two greatest risk factors for breast cancer are being a female and getting older. Breast density is one of many risk factors.

A recent large scale study shows breast density is a more significant risk factor than family history. The greater the density, the higher the risk of getting breast cancer.  

Women with the highest level of density (Category D: >75% dense tissue) are 4-6 times more likely to get cancer than women with the lowest (Category A: <25 % dense tissue).  

As well, since mammograms detect about 50% of cancers in dense breasts vs. 98% in fatty breasts, cancer found in dense breasts is usually detected at a later stage, possibly making prognosis worse.

Boyd, N., Guo, H., Martin, L., Sun, L., Stone, J., Fishel, E., Jong, R., Hislop, G., Chiarelli, A., Minkin, S., and Yaffe, M.  (2007, Jan.). Mammographic density and the risk and detection of breast cancer. New England Journal of Medicine, 356:227-236.  View Study

Engmann N, Golmakani M, Miglioretti D, Sprague B, Kerlikowske K, for the Breast Cancer Surveillance Consortium. (2017, Feb 2.)Population-Attributable Risk Proportion of Clinical Risk Factors for Breast Cancer. JAMA Oncol.   View Study

What If I Have Dense Breasts?

Discuss your density category and any other risk factors such as genetics, family history, and previous biopsies so that your overall cancer risk is understood.

What should I discuss with my healthcare practitioner?

Discuss your density category and any other risk factors such as genetics, family history, previous biopsies, etc. so that your overall cancer risk is understood. Evidence shows dense breasts are a more significant risk factor for breast cancer than family history.

If you have dense breasts, talk to your doctor/nurse practitioner about having additional screening, such as ultrasound because a "NORMAL" mammogram result may not be accurate. Dense tissue can mask cancer. Ultrasound finds additional cancers. You are the best advocate for your health and you may need to advocate for additional testing.

HOW TO ADVOCATE FOR ADDITIONAL SCREENING
It is NOT Canadian protocol to order a screening ultrasound for women with dense breasts unless an abnormality has been detected by mammogram or clinical examination. Yet, we know early detection is key.

If you want added screening, advocate for yourself and let your doctor/nurse practitioner know you are aware of the following risks:

  • The increased cancer risk associated with dense breasts. Dense breasts are an independent risk factor. Dense breasts are a more significant risk factor than family history.
  • The unreliability of mammography for dense breasts because of the dense tissue camouflaging effect
  • The high level of interval cancers for women with dense breasts- cancers detected in between screenings
  • The proven ability of ultrasound and MRI to detect additional cancerous tumours missed by mammogram

Remember: In most cases, when extra screening is done, women are NOT found to have breast cancer.

5 steps you can take right now to minimize your risk.
  1. Speak with your doctor about your breast density, all breast cancer risk factors and your best screening options.
  2. Perform regular self-exams between screenings. A normal mammogram result may not be accurate.
  3. To improve early detection, consider additional screening, such as ultrasound and/or MRI.
  4. Consider modifying lifestyle factors such as diet, exercise, alcohol intake and hormone use to decrease cancer risk.
  5. Continue to have mammograms because they can detect calcifications, which can be the earliest sign of cancer.
Why is ultrasound beneficial for women with dense breasts?

Ultrasound can detect a small cancer in an early stage before it spreads to lymph nodes.

In women with dense breasts, studies show that for every 1000 women screened, ultrasound finds another 3-4 cancers that were not seen on mammogram.

Several large studies have shown that supplementing mammograms with ultrasound can increase detection up to 97% in women with dense breasts.

Berg, W, Blume, J., Cormack, J. et al. (2008). Combined screening with ultrasound and mammography vs. mammography alone in women at elevated risk of breast cancer. JAMA, 299: 2151-63. 

Why isn't ultrasound used for women with dense breasts?

Ultrasound is used when an abnormality is detected by mammogram or clinical exam. It is not used routinely for screening because it is a sensitive test and can sometimes result in false positives –  an abnormality that is not cancer. False positives are inevitable in screening and very few tests will show cancer. If you want to have an ultrasound, ask and advocate for yourself. Ultrasounds, in addition to mammography, are important for women with dense breasts because mammograms can miss cancers due to the masking effect of dense tissue.

What if my practitioner won't order additional screening?

 

If you have dense breasts and would like an ultrasound, but your doctor/nurse practitioner will not order it, you can look into private facilities in your province that offer ultrasound without a doctor’s requisition.

Ontario Residents: There are three private clinics offering 3D Automated Breast Ultrasound (ABUS). Private insurance may cover some of the cost. Clinics are located in Toronto and Barrie. ABUS was approved by Health Canada in 2011 as a screening tool. You do not need a doctor’s/nurse practitioner’s referral. More information about private options can be found in the Screening Options Section.

BC Residents: UPDATE January 2019.  Screening ultrasound for women with dense breasts is now covered by MSP if your doctor/nurse practitioner is prepared to give you an ultrasound. If not, there are imaging facilities that provide hand held ultrasound without a requisition. If you do not have a requisition, screening ultrasound is an out of pocket expense in BC (around $250).

 

 

What is 3D ultrasound-ABUS?

3D ultrasound, also know as Automated Breast Ultrasound (ABUS) uses sound waves. Thousands of images are created and software reconstructs images in 3D.

Automated Breast Ultrasound (ABUS) was approved by Health Canada as a screening tool and as an adjunct to mammography for women with no symptoms for breast cancer. Evidence shows it finds an additional 3.6 cancers per 1000 women screened. It is currently available privately in Ontario (Toronto and Barrie)  and under provincial insurance in Alberta.

3D Automated Breast Ultrasound (ABUS) can increase the rate of breast cancer detection by 35.7% in women with dense breast tissue.  

Some private insurance plans pay a portion towards the use of ABUS. Please check with your provider. More information about where you can access ABUS can be found below.

There are three private clinics offering 3D Automated Breast Ultrasound (ABUS) in Ontario. Private insurance may cover some of the cost. Clinics are located in Toronto and Barrie. ABUS was approved by Health Canada in 2011 as a screening tool. You do not need a doctor’s/nurse practitioner’s referral.

Should I continue to get mammograms if I have dense breasts?

YES! Mammograms are proven to reduce breast cancer deaths. Mammograms can reliably detect suspicious calcifications. Ultrasound/ABUS do not replace mammograms; they should be used in addition to mammography.

How do I calculate my risk?

A breast cancer risk calculator is a tool that can help you and your doctor better understand your risk and make informed decisions. We’re posting the TYRER-CUZICK 8 model because it’s just been updated to include breast density as a risk factor. It’s a well-studied and widely-used model that is easy and quick. Just click Imperial Units and if you know your density click BIRADS. If you don’t know your density, you can still use it and retry it when you find out your density. The model calculates 10 year risk and lifetime risk. Check it out.

What If I Have Dense Breasts?
Female doctor discussing with a patient

Screening Methods for Canadian Women with Dense Breasts

The following screening tests are described below:  Mammography, Ultrasound, 3D Ultrasound (ABUS), MRI, Tomosynthesis.

Why is additonal screening needed?

Mammography reduces mortality from breast cancer, but it is an imperfect screening tool for women with dense breasts because it misses cancerous tumors in dense breasts.

Mammograms can miss cancer about 50% of the time in the densest breasts. Therefore, women with dense breasts might want to consider additional screening with their mammogram. Ultrasound or MRI, when combined with mammography, significantly improves the rate of cancer detection in women with dense breasts.

In Canada, additional screening is not easily accessed. You may need to advocate for yourself.

Mammography

What it is: Mammography x-rays the breast from different angles. A mammogram is the only way to find out breast density.  

Positives:  Over the past 30 years, mammography has helped reduce deaths through early detection by more than 35%.

Limitations: For women with dense breasts, dense tissue and cancer appear white on a mammogram, making it hard for cancer to be seen. Mammography uses low-dose radiation.

Accessibility: Screening mammography is available across Canada, except Nunavut. Digital mammography is widely available and is more accurate than analog mammography in dense breasts.

 

why breast density matters

Ultrasound

What it is: Ultrasound uses high frequency sound waves to image the breast. 

Positives: When used with mammography, ultrasound increases the rate of cancer detection up to 97%. It detects an additional 3-4 cancers per 1000 women. It can detect cancer in dense breasts at an early stage. It is quick, safe, and non- invasive. No radiation is involved.

Limitations: Ultrasound is a very sensitive test and is generally used for diagnostic purposes, not screening. It may identify abnormalities that require additional investigation. Ultrasound alone is not recommended as a breast cancer screening tool.   

Accessibility: A requisition for ultrasound is not usually given unless there has been a suspicious finding on a mammogram, MRI or a clinical breast exam.  There may be a private clinic in your city where you do not need a doctor’s/nurse practitioner’s requisition and can pay directly. UPDATE: IN BC: Screening ultrasound is now covered by MSP for women with dense breasts if the family doctor/nurse practitioner is prepared to give the woman a requisition. 

Automated Breast Ultrasound (ABUS)-3D Ultrasound

What it is: This is a 3D ultrasound. Sound waves and software reconstruct breast images in a 3D plane.

Positives: ABUS can find small, invasive, node-negative cancers missed by mammography. ABUS was found to detect an additional 3.6 cancers per 1,000 women screened after mammography.When used with mammography, its effectiveness is from 94 to 97%. It is radiation free.

Limitations: ABUS may identify abnormalities that are not seen on a mammogram. Some of these abnormalities may require additional ultrasound or biopsy. Remember to resist the extra anxiety of false positives because most abnormalities are not cancerous.

Accessibility: Currently, ABUS can be found in Ontario and Alberta

In Ontario, patients must pay out of pocket for ABUS, but some private/group insurance plans may cover part of the cost. ABUS can be found in 2 locations in downtown Toronto and also in Barrie.

In Alberta, ABUS is covered under the provincial health insurance plan (AHIC) for women with dense breasts who qualify. A number of clinics offer ABUS.

 

Magnetic Resonance Imaging (MRI)

What it is: It uses magnetic fields, radio frequency pulses, and a computer to produce detailed images of the breast..

Positives: MRI detects the most breast cancers of any imaging. It is an effective screening tool for women with dense breasts and detects 18 or more additional cancers per 1000 women. No radiation is involved.  MRI is generally recommended for women with the highest cancer risk (those who carry the breast cancer gene, women who have had chest wall radiation for treatment of lymphoma, and some with rare genetic diseases)

Limitations: MRI is likely to generate more false positives requiring biopsy. It requires intravenous contrast injection.

Accessibility: MRI is available across Canada, but it is not used as a screening tool. It is currently used along with mammography for high-risk patients (BRCA gene, strong family history, or history of radiation to chest).  There are a number of private pay MRI locations in Canada, but a physician’s referral is required.

 
 

Tomosynthesis

What it is: Also known as 3D mammography, it creates multiple thin slices of images so that overlapping tissue is less likely to hide a cancerous tumour. The patient is positioned exactly the same way as for standard mammography.

Positives: Tomosynthesis increases the detection of invasive tumours over digital mammogram by an additional 1-2 cancers per 1000 women.  When used with mammography, it decreases the false positive rate.

Limitations: Tomosynthesis does not detect as many cancers in dense breasts as ultrasound. The radiation dose may be higher than regular mammography because image acquisition takes longer. When used along with regular mammography, the radiation dose is slightly more than double.

Accessibility: Currently, Tomosynthesis is mostly being used for diagnostic purposes after an abnormality is found. However, In Alberta, patients visiting certain clinics are screened with both 2D mammography and tomosynthesis. Clinical studies are taking place in Canada to evaluate the role of tomosynthesis in screening for breast cancer.

 

Finding Out My Density

How you can find out your breast density in your province.

If you have had a mammogram, here’s how you can find out your breast density in your province.

BRITISH COLUMBIA:
Breast density notification was implemented on Oct.15, 2018. You will be informed of your breast density category in your mammogram results letter: A, B, C or D. Category C and D are dense breasts. If your mammogram was prior to Oct.15, 2018: You can find out your density by using this “Access to Information” form
http://www.bccancer.bc.ca/…/SMP_Form-SMPRequestForAccessToR… Under “Requested Info" write: “I want to know my breast density category."

News: Screening ultrasound is now covered under MSP for women with dense breasts, if the healthcare provider provides a requisition. In Vancouver, screening ultrasound is available at: X-Ray 505, Downtown Radiology, North Shore Imaging, BC Women’s and other clinics.


ALBERTA:
Your healthcare provider receives a report that has a description of your density in words or letters, Category A, B, C or D. You can ask your provider what your report says. Alberta is working on formalizing direct breast density notification for all women. There are clinics in Alberta, such as Mayfair, Canada Diagnostics, EFW, Pureform Radiology and MIC Medical Imaging that offer screening ultrasound to women with dense breasts, paid for by Alberta Health Services. News: AHS is implementing personal health portals, “My Health Records,” where you can sign up to access your medical reports, including your mammogram report.


SASKATCHEWAN:
Breast density notification was implemented for women with >75% density in Nov. 2018.
You will be informed of your density category in your mammogram results letter ONLY if your density is over 75%. You will be asked to return annually for a mammogram. Your healthcare provider is also told if your density is over 75%. However, dense breasts refer to breasts with 50% and over dense tissue. Women in the 50-75% category are not told they have dense breasts because this information is not recorded. We continue to advocate, and if you would like to express your concern about the withholding of information from women in the 50-75% category, please contact the Health Minister, The Honourable Jim Reiter: He.minister@gov.sk.ca


MANITOBA:
In June, you will be informed of your density category in your mammogram results letter ONLY if your density is over 75%. Your healthcare provider will also be told if your density is over 75%. However, dense breasts refer to breasts with 50% and over dense tissue. Women in the 50-75% category are not told they have dense breasts because this information is not recorded. If you would like to express your concern about the withholding of this information, please contact the Health Minister, The Honourable Cameron Friesen. minhsal@leg.gov.mb.ca


ONTARIO:
You will be informed by mail of your density only if your density is over 75%. You will be asked to return annually for a mammogram. Your healthcare provider will also be told if your density is over 75%. However, dense breasts refer to breasts with 50% and over dense tissue. Women in the 50-75% category are not told they have dense breasts because this information is not recorded. However, some radiologists in Ontario describe the density category in words on the cover letter sent to the healthcare provider. Please ask your provider if any additional information has been supplied. We continue to advocate in Ontario and if you would like to express your concern about the withholding of information from women with dense breasts in the 50-75% category, please contact the Health Minister: The Honourable Christine Elliott
Christine.elliott@pc.ola.org


QUEBEC:
Your mammogram report sent to your healthcare provider has a description of your density in percentages. Every report has the density. You will NOT be notified directly but you can find out your density by asking. The density information is on the third line of the report. Women with over 75% density and a family history are offered screening ultrasound. We continue to advocate for direct notification and if you would like to express your concerns about the withholding of information, please contact The Health Minister, The Honourable Danielle McCann
ministre.responsable@msss.gouv.qc.ca


NOVA SCOTIA:
The government has committed to breast density notification and it is likely to begin in Fall 2019.
All women will be notified of their breast density category in their mammogram results letter. Until notification begins, no information is provided to women or healthcare providers. These are the steps you can take to find out your density: On a breast screening requisition, ask your healthcare provider to write: “Please review patient’s mammogram images and inform me of the patient’s density.” Fax the form to the central booking office at 902 473 3959. There is no fee. The request can be made for mammograms done in the past, as well as those being ordered now.


NEW BRUNSWICK:
The government has committed to breast density notification for all women and it is expected to begin later in 2019. Currently, your mammogram report sent to your health care provider has a description of your density in words or percentages. To learn your density, you can ask your healthcare provider what the report says.

PEI
The government has committed to breast density notification for all women and ultrasound for women with over 75% density (Category D). We do not have an implementation date as of yet. Currently, healthcare providers are notified if the breast density is 75% and over. Women with over 75% dense tissue are recalled annually for a mammogram. Women with dense breasts in the 50-75% category are not told they have dense breasts because this information is not recorded. We hope to see this changed soon with the new government's commitment to notifying all women. 


NEWFOUNDLAND/LABRADOR:
You are not provided with any information. Your healthcare provider is notified if the breast density is over 75%. Women with over 75% density are asked to return for an annual mammogram. However, dense breasts refer to breasts with 50% and over dense tissue. Women in the 50-75% category are not told they have dense breasts because this information is not recorded. We continue to advocate, and if you would like to express your concern about the withholding of information from women in the 50-75% category, please contact the new health minister after the May 16th election.


NWT and YUKON
You are not provided with any breast density information. Your healthcare provider is notified if the breast density is 75% and over. Women with dense tissue in the 50-75% category are not told they have dense breasts because this information is not recorded. In NWT, women with over 75% density are asked to return for annual mammograms.

Finding out my density

Medical Disclaimer

The Dense Breasts Canada website is intended for the general purpose of:
1. Raising awareness about dense breasts and
2. Encouraging advocacy for the reporting of dense breast tissue to women.
We have included references, where applicable to ensure that the information provided is evidence based. However, we cannot guarantee that the information on the site is error-free or complete. The website is not intended to be a substitute for medical advice from a doctor. For answers to specific health-related questions, please consult your doctor. While we speak of Automated Breast Ultrasound (ABUS), we are not affiliated in any financial way with any private clinics that offer ABUS.