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Breast Density: the breast cancer risk factor no one talks about

by Jennie Dale, Cancer Survivor, Co-founder Dense Breasts Canada


Joanne Brennan, of Ottawa, has Stage 4 breast cancer. And she is furious.


“I didn’t know to ask if I had dense breasts. If I had, I might not be what I am today, dying from Stage 4 breast cancer. It is the doctor’s responsibility to tell you if you have dense breasts, but our doctors are not telling patients,” she says. “There’s a big gap. It’s not just about being breast cancer aware, it’s about knowing what to ask.”


Joanne is far from alone. In fact, the majority of Canadian women with dense breasts are being left in the dark about their density and the risks that come with it. They are unaware of the impact dense breasts can have on cancer detection and prognosis.


Dense Breasts Canada, a group of Canadian women with breast cancer, is working to encourage provincial cancer agencies and doctors to tell women about their breast density – and to get women to ask their doctors if they aren’t told.


Unlike the United States, there are currently no guidelines in Canada for the reporting of breast density. In some provinces, breast density information is never shared with the family doctor or patient. In other provinces, breast density information is stated in the mammogram report that the family doctor receives, but this information is rarely discussed with the patient.


What are dense breasts?

Dense breasts are normal and common; they are simply breasts that have more glandular tissue than fat. Roughly 43% of women, over age 40 have dense breasts. [i]  The radiologist reading your mammogram uses one of four categories to describe breast density in percentages or words. If you have more than 50% dense tissue, you have dense breasts. The words: “heterogeneously dense breasts” and “extremely dense breasts” also describe dense breasts. There are some common misconceptions: first, lumpy breasts are not dense breasts and second, density is not about size or firmness. You cannot tell density by look or feel; only a radiologist can assess breast density.




Here’s why knowing and understanding your density matters:


  1. Women with dense breasts have a higher chance of developing breast cancer:  Dense breasts are an independent risk factor for cancer. Women with the densest breasts are 4-6 times more likely to get cancer.[ii]  While women are often aware that they are at an increased risk because of a family history, they are unaware that dense breasts are an even more significant risk factor than a family history.[iii]


  1. The accuracy of a mammogram is impacted by dense breast tissue:  Dense breasts are the number one reason for cancer being missed by mammography.  In women with fatty breasts, mammograms are 98% accurate, but in women with dense breasts, mammograms may be less than 50% accurate because both cancer and dense tissue show up white on a mammogram image.[iv] A camouflage effect is created.


  1. Higher risk of cancer in the other breast: Women who’ve been diagnosed with breast cancer and have dense breasts are nearly twice as likely to develop cancer in the opposite breast.[v]


  1. Higher risk of an interval cancer: Women with dense breasts are 18 times more likely to present with an interval cancer (a cancer that becomes ‘feelable’ after a mammogram that is read as ‘negative’). [vi]  Interval cancers are larger, rapidly growing and have a much worse prognosis than mammogram-detected cancers.


What to do if you have dense breasts:

Find out your density by asking your doctor. If your doctor does not have the information, fill out an access to health information form and send it to your provincial screening agency. If you learn you have dense breasts, understand that mammograms are not enough. As Dr. Paula Gordon, Medical Director of BC Women’s Hospital Breast Program, points out, “Women with dense breasts should consider a supplemental method of screening, such as ultrasound, in addition to their mammogram. Ultrasound finds an additional 3-4 cancers per 1000 women screened. [vii]  Ultrasound is shown to detect small, node-negative cancers. Studies show that breast cancer mortality correlates with invasive tumour size and node status. [viii]  Therefore, diagnosis of breast cancer at an early stage is vital. If women are told they have dense breasts, they have the chance to be vigilant about their breast health in terms of supplementary screening and self-check.”


Victoria resident Ellen Coburn discovered a lump during a self-exam. Nothing suspicious showed on her mammogram; it was an ultrasound that detected the cancerous tumor. Ellen writes: “I am very concerned by the false sense of security that comes with getting an ‘all clear’ mammogram. If you have dense breasts, there is a real possibility that things can be missed! I am also concerned that I was not warned that the level of density increased my risk of breast cancer, and that it was even higher than having a direct family member with the disease. Women need to know this!! And access to this information shouldn’t be dictated by what province you live in!”


Dense Breasts Canada (DBC) is advocating for all provincial governments to report breast density, and for health providers to deliver supplemental screening, such as ultrasound, for women with the densest breasts. Until there’s a cure, all women with breast cancer should have the right to find it when it’s small.  For more information on dense breasts visit




[i] Sprague, B., Gangnon, R., Burt, V., Trentham-Dietz, A., Hampton, J., Wellman,  R., Miglioretti, D. (2014). Prevalence of Mammographically Dense Breasts in the United States. JNCI Journal of the National Cancer Institute, 106 (10),

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.

 [iii]  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.

[iv]  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.

[v] Raghavendra, A., Sinha, A. K., Le-Petross, H. T., Garg, N., Hsu, L., Patangan, M., Bevers, T. B., Shen, Y., Banu, A., Tripathy, D., Bedrosian, I. and Barcenas, C. H. (2017). Mammographic breast density is associated with the development of contralateral breast cancer. Cancer, 123: 1935–1940.

[vi] Boyd, N., Martin, L.,  Yaffe, M and Minkin, S. (2011).Mammographic density and breast cancer risk: Current understanding and future prospects Breast Cancer Res 13:223

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.

[viii] Saadatmand, S.,Bretveld,R., Siesling,S., Tilanus-Linthorst,M. (2015, Oct. 6). Influence of tunor stage at breast cancer detection on survival in modern times:population bases study in 173787 patients. The BMJ.




Jennie Dale is a co-founder of Dense Breasts Canada.  She was diagnosed with breast cancer in 2014. Mammography failed to detect her breast cancer. However, she was fortunate that ultrasound screening did. She was inspired to reach out to breast density advocacy organizations and discovered Canada was not doing enough to protect women with dense breasts from being diagnosed with later stage breast cancer. Jennie teamed up with other breast cancer survivors whose lives have been affected by a delayed breast cancer diagnosis due to cancer being obscured behind dense breast tissue. She is working with Dense Breasts Canada to raise women’s awareness about the importance of knowing their breast density, to advocate for provincial governments to report breast density to women, and to provide supplemental screening for women with the densest breasts. For more information visit:



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