Frequently Asked Questions
What Is Breast Density?
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. (see Finding out my Density).
UNDER 25% dense tissue OR Category A OR 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 OR Category B OR 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 OR Category C OR 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 OR Category D OR 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" BREASTS 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.
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
AROMOTASE INHIBITORS AND TAMOXIFEN: The use of these cancer drugs decreases density
WHAT IF I DO NOT 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.
Why Does My Breast Density Matter?
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 MY 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
Why Does It Matter What Province I Live In?
HOW CAN I FIND OUT MY DENSITY IN MY PROVINCE?
There is wide variation in the way provinces report on breast density following a screening mammogram**.
- In some provinces, you can just ask your doctor/nurse practitioner what the mammogram states about your breast density and the information may be available. Or it may not.
- In some provinces, your doctor/nurse practitioner has not been told.
- In some provinces, there is no way for all women to find out their density.
If you live in BC: You and your doctor/nurse practitioner will be notified of your breast density in your results letter, as of Oct. 15, 2018. If you are not due for another mammogram for awhile, you can send in this “Request for Access to Records” form to find out: https://bit.ly/2sM6mLf (See Finding out my Density for more info).
If you live in MB: Your doctor/nurse practitioner is not told your density. It is worthwhile to send in a Request to Release Personal Health Information form. However, information is only available for women assessed as Category D:75% and over dense tissue. You cannot find out if you are in Category C: 50-75% , which is also considered dense breasts because this information is not recorded. You can advocate to have your mammogram assessed using all 4 categories of density. (See Finding out my Density for form).
If you live in SK, PEI, ON, NWT, YT, NL: You and your doctor/nurse practitioner are only notified if you have 75% and above dense breast tissue. There is no way to find out if you are in the 50-75% density category which is also considered dense breasts. You can advocate to have your mammogram assessed using all 4 categories of density (See Finding out my Density Section).
If you live in Quebec: Your breast density information is in your mammogram report. Ask your family doctor/nurse practitioner what category you are in and if you have dense breasts, discuss the risks. Women in Category D with a family history are referred for a screening ultrasound.
If you live in the other provinces: your family doctor/nurse practitioner may or may not have the information. It depends if the radiologist who reads your mammogram has shared the information. You need to ask your doctor/nurse practitioner what your mammogram report says to see if the information is there.
**The information applies to a screening mammogram, not a diagnostic mammogram. It applies only to women being screened under their provincial breast screening programs.
|Density is NOT reported to family doctor||Women with 75% and over dense tissue are asked to return for a mammogram in 1 year instead of 2||Density is sometimes but not always described in report to family doctor|
|Manitoba||Newfoundland||Alberta (will be in all reports as of Summer 2018)
|Nova Scotia||Ontario||British Columbia (always)|
|Saskatchewan (only if patient has over 75% density)||NWT||New Brunswick
|Newfoundland (only if patient has over 75% density)||PEI
||Quebec (ALWAYS- it is mandatory)
|PEI (only if patient has over 75% density||Yukon (only as <75% and over 75%)
|NWT (only if patient has over 75% density)||Newfoundland (only if patient has over 75% density)
What Should I Do If I Have Dense Breasts?
WHAT SHOULD I DISCUSS WITH MY DOCTOR/NURSE PRACTITIONER ? HOW DO I ADVOCATE FOR SCREENING?
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. A reminder: evidence shows dense breasts are a more significant risk factor for breast cancer than family history (Engmann et al, 2017).
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.
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. http://www.ncbi.nlm.nih.gov/pubmed/18477782
IF ULTRASOUND IS BENEFICIAL, WHY IS IT NOT PROTOCOL 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 DOCTOR/NURSE PRACTITIONER WILL NOT 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 - AUTOMATED BREAST ULTRASOUND (ABUS)?
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 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 in the Screening Options Section
SHOULD I CONTINUE TO GET MAMMOGRAMS IF I HAVE DENSE BREASTS?
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.
CALCULATING 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. http://ibis.ikonopedia.com/
ADDITIONAL SCREENING OPTIONS FOR CANADIAN WOMEN WITH DENSE BREASTS
The following screening tests are described below: Mammography, Ultrasound, 3D Ultrasound (ABUS), MRI, Tomosynthesis.
Why is additional 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.
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.
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)
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.
MRI (MAGNETIC RESONANCE IMAGING)
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.
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.
Dr. Paula Gordon: Breast Cancer: Screening, Prevention & The Importance of Breast Density
Breast Density: What’s all the fuss about? By Wendy Ingman
InforMD: a new initiative to raise public awareness about breast density
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.