What Is Breast Density?

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 prevalent 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
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 prevalent risk factor than family history.
• The unreliability of mammography for dense breasts because of the camouflaging effect. Both cancer and dense tissue appear white on a mammogram. This affects both categories of dense breasts.
• The high level of interval cancers for women with dense breasts- cancers detected in between screenings when a woman feels a lump after a negative mammogram.
• 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.

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 (or MRI if you are considered high risk).
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.

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 2-3 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.

It has been known since 1995, when the journal Cancer published the first paper, that ultrasound detects small, invasive node negative cancers in women with dense breasts.

An RCT of supplementary ultrasound screening is underway in Japan, and is showing greater cancer detection, and reduced interval cancers.

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. 

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.

If you have dense breasts and would like an ultrasound, but your doctor/nurse practitioner will not order it, please check out our conversation tips on what to say. To advocate effectively, we have prepared this list of potential arguments you may face. Science is on your side and decades of evidence showing the benefits of ultrasound. Here is the tip sheet. https://www.densebreastscanada.ca/wp-content/uploads/2022/02/Script-for-women-with-dense-breasts-who-want-a-screening-ultrasound.pdf

If you like, you can look into private facilities in your province that offer ultrasound without a doctor’s requisition.

Ontario Residents: There is a private clinic in Toronto 3D Automated Breast Ultrasound (ABUS). Private insurance may cover some of the cost.  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).

You have dense breasts and are denied a screening ultrasound or want an ultrasound. So, you’ve had a mammogram and learned you have dense breasts. Since dense tissue can mask cancer on a mammogram, you would like additional screening. You need a requisition for a screening ultrasound, but your health care provider will not provide one or needs to be convinced. We’ve designed a script to help you advocate for yourself and overcome any potential barriers while having a conversation with your health care provider.

If your health care provider says: The Canadian breast cancer screening guidelines do not recommend screening ultrasounds for women with dense breasts.

You can respond: I understand that is the recommendation but since there is an increased cancer risk with dense breasts and since mammograms are not as effective because of the masking effect, I would like to schedule an ultrasound to be safe.

Additional information: Since 1995, ultrasound has been proven in multiple studies to detect additional cancerous tumours missed by mammogram.[1]

If your health care provider says: You don’t have a family history or any other risk factors and so you don’t need to worry about additional screening.

You can respond: Dense breasts are actually a more prevalent risk factor than family history.[2] Most women diagnosed with breast cancer have no risk factors they are aware of. I would like to go ahead and schedule an ultrasound.

**If it applies to you, you can remind your health care provider that Black, Asian and Hispanic women are at an increased risk for breast cancer at a younger age than white women.[3]

If your health care provider says: Having a screening ultrasound can result in a “false positive”, meaning you will be recalled for more testing. These tests can create anxiety for you.

You can respond: I understand that there’s a chance that more tests will be needed if something is picked up, but I’m not very worried about being recalled. I’d rather be safe than sorry. I understand any anxiety I experience will be short-lived if I have a normal result. And if the result is not normal, I’d prefer to have cancer found at an early stage, rather than a later stage. I would like to go ahead and schedule an ultrasound.

[1] https://acsjournals.onlinelibrary.wiley.com/doi/abs/10.1002/1097-0142(19950815)76:4%3C626::AID-CNCR2820760413%3E3.0.CO;2-Z
[2] https://jamanetwork.com/journals/jamaoncology/article-abstract/2599991
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5875337/?tool=pmcentrez&report=abstract 

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 in 2011 and as an adjunct to mammography for women with no symptoms for breast cancer. Evidence shows it finds up to an additional 3.6 cancers per 1000 women screened. It is currently available privately for screening in Toronto. It is readily available in Alberta and paid for under provincial insurance.

Private insurance may cover some of the cost in Ontario.  You do not need a doctor’s/nurse practitioner’s referral if you are paying privately in Ontario.

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.

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. You can do the calculator on  your own and message us if you have any questions. 

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. In AB, lifetime risk over 20% is considered high risk and in ON and NS , 25% lifetime risk is considered high risk and there is a specialized high risk program in NS and ON. Elsewhere: If your lifetime risk is over 20 or 25% please speak to your provider about policies in your province  Check out calculator here.

Women who have breast cancer are at higher risk of getting a second cancer in the same breast or the opposite breast. Women who have breast cancer and have dense tissue are at higher risk of getting breast cancer in the other breast than a woman with non-dense breasts. Patients with high density have a much greater risk of local recurrence compared with women with the least dense breasts (21% compared with 5%).

The American College of Radiology now recommends screening with mammography and MRI for women who’ve had cancer, who have dense breasts, or for women who were diagnosed with cancer before age 50, with all breast densities.

These recommendations are not routine in Canada, but experts recommend you advocate for yourself.

Check out DBC's Advocacy Tool Kit to help you advocate for the screening you need.

The information below shows some of the latest evidence on the benefits of additional screening. Feel free to copy, paste and print for your doctor.

Women with Dense Breasts Deserve the Right to Effective Screening

1. Background
   Canadian provinces and territories inform women of their breast density category. However, notification alone is not enough—women with dense breasts need supplemental screening, such as ultrasound, CEM, or MRI, for early cancer detection. Both category C and D women face increased risk and require additional screening to ensure early diagnosis and better outcomes.

2. Risks of dense breasts

Dense breasts are normal and common but carry two significant risks:

1. Increased cancer risk: Women with the densest breasts (category D) are four to six times more likely to develop breast cancer than those with fatty breasts (category A).
2. Masking: Dense breasts make it harder for radiologists to spot cancer because both cancer and dense tissue appear white on a mammogram. The denser the breast, the greater the possibility that cancer will be missed on a mammogram. In fact, mammography misses 40% of cancers in women with category D density and 30% in category C.

Cancers missed on mammograms continue to grow and are often discovered only when a lump is felt. These are known as interval cancers, diagnosed between scheduled screenings. Interval cancer rates are 13 to 18 times higher in women with dense breasts and these cancers tend to be larger and more likely to have spread to lymph nodes. Consequently, these women often need more aggressive treatments and have poorer outcomes compared to those with screen-detected cancers. The purpose of screening is to detect cancers early to reduce deaths and suffering. Therefore, reducing interval cancers is a critical goal.

Individuals with non-dense breasts who undergo mammograms are 41% less likely to die from breast cancer compared to those who do not. In contrast, women with dense breasts who have mammograms are only 13% less likely to die. This disparity represents a life-threatening inequity, as individuals with dense breasts in Nova Scotia are underserved if mammograms are their only screening option.

3. Evidence on supplemental screening: MRI, CEM, and Ultrasound

To reduce interval cancers effectively, supplemental tests like ultrasound or MRI should be offered. These modalities are proven to detect cancers missed by mammography when they are small and have not yet spread, and before they become interval cancers.

i). MRI Screening Supporting Studies:

• MRI has been proven to detect invasive cancers and reduce both interval cancers and late-stage disease in many studies.
• The DENSE trial in the Netherlands, an ongoing RCT, published results showing the interval cancer rate dropped to 0.8/1000 when MRI was added to mammography, compared to 4.9/1000 with mammography alone.
• A study from Memorial Sloan Kettering involving 2780 women at elevated risk screened with MRI and mammography showed no interval cancers, compared to 9 interval cancers among 4811 women screened with mammography alone.
• A Canadian study demonstrated a reduction in late-stage disease due to MRI screening in women with known pathogenic variants.
• MRI screening has increased the detection of biologically significant cancers.

Surrogate for Mortality Reduction: Reduction of interval cancers is considered an acceptable surrogate for breast cancer mortality reduction, which typically takes over 10 years to demonstrate in an RCT. In Europe, MRI is recommended for all women aged 50-70 with category D density. MRI is effective in finding more cancers than ultrasound. However, the focus on mortality alone overlooks the broader benefits of early detection.  Early detection of breast cancer means a better prognosis, less aggressive treatment, better quality of life, and less cost to the healthcare system.

ii). Ultrasound Screening Supporting Studies:

• Research over the past three decades, including single-institution and multi-centre trials, has shown that supplemental ultrasound screening benefits women with dense breasts by improving the detection of node-negative invasive cancers and reducing interval cancer rates.
• Studies have shown that ultrasound detects an additional 2-3 cancers per 1000 examinations over mammography alone.
• The J-Start trial in Japan, an RCT that began in 2007, has shown that adding ultrasound to mammography finds more cancers, which are smaller and have not yet spread to the lymph nodes. The trial indicated that adding ultrasound reduced interval cancers by a factor of 4, with an interval cancer rate of 0.5/1000 in the group having mammography plus ultrasound compared to 2.0/1000 in the control group.
• Predictive Metrics: The decreased interval cancer rate in the study suggests a predicted reduction in mortality.
• It is unethical to allow women to die while waiting for RCTs in Japan and the Netherlands to mature, especially given the significant findings to date.

iii). Braid study-uk: A randomized control trial in UK recently published included 9000 women with dense breasts and negative 2D mammogram. They were randomized to 1 of 4 screening groups for supplemental screening; abbreviated MRI (Ab-MRI), automated whole breast ultrasound (ABUS), contrast-enhanced mammography (CEM), or no supplemental screening. All modalities significantly increased cancer detection. All cancers detected were small. Cancer detection rates for Ab-MRI, ABUS, and CEM were 17.4/1000, 4.2/1000, and 19.2/1000, respectively and recall rates were 9.7%, 4.0%, and 9.7%, respectively .

iv). Ontario Health report: In December 2023, Ontario Health released a comprehensive 293-page “Health Technology Assessment” on supplemental breast cancer screening. This assessment recommended supplemental screening due to its effectiveness in detecting more cases of breast cancer and reducing interval cancers in women with dense breasts (categories C and D). However, due to cost considerations, Ontario Health recommended publicly funding supplemental screening only for category D. At the time of the study, the cost analysis (Table 1) had not yet been published.

Currently, women with category D breast density in Ontario can request a requisition from their provider for an MRI every two years or an ultrasound every year, in addition to their mammogram, while the Ontario screening program works to make supplemental screening standard for category D.

v). Two studies from British Columbia: Research from British Columbia reveals seven additional cancers per thousand screenings that were not detected by mammography. Mammography typically finds five cancers per thousand. The additional seven cancers, missed by mammograms, would likely have progressed to interval cancers.

Another important Canadian study, recently published, shows that using ultrasound for women with dense breasts for both screening and surveillance after cancer, finds six cancers per thousand screens. This is more than double the rate in most other published studies, primarily from the USA. This is, partly because in the US, women have annual mammograms, whereas in Canada, most women only have biennial mammograms, and because in the US, screening mammography is increasingly done with 3-D technology. So, there are more cancers, not found on mammography in Canada than in the US.

4. Cost savings in treatment from early detection

MRI as a supplemental screening tool effectively reduces interval cancers, making it cost effective. That is part of the rationale used by EUSOBI and Ontario Health to recommend breast MRI for women with category D breasts. The cost of treating advanced cancer has increased exponentially in the last several years, driven by the high cost of new, beneficial drugs. Recently published Canadian research shows that there are large reductions in treatment costs when cancers are detected earlier.  Table 1 shows the cost of treatment by stage and subtype. The mean treatment cost for a Stage 1 patient is $39,000, compared to $371,000 for a Stage 4 patient. For women with Her2-positive Stage 4 cancer, treatment costs can exceed $500,000.

5. Jurisdictions

Canada: Residents of British Columbia, Alberta, Saskatchewan, NWT, or Ontario, can access supplemental screening to varying degrees. Outside of Canada: Many US states are offering supplemental screening. As well, as shown in the chart compiled by DenseBreast-info.org, several countries have made supplemental screening a standard practice.

6. Recommendations

The benefits of supplemental ultrasound, CEM, or MRI for early detection in individuals with dense breasts are evidence based. These screenings significantly reduce interval cancer rates, as confirmed by robust research.

Given the clear evidence supporting additional screening for those with dense breasts, it's time for all provinces/territories to align with leading practices and ensure equitable access to early detection methods for all. Not only would this promote health equity but also reduce healthcare costs and the burden of late-stage cancer treatment.