Millions of Canadian women have dense breasts. Most women don’t know what their breast density status is
and don’t understand the potential implications of having dense breasts. Having dense breasts is completely normal; research suggests that about 40% of women over 40 have dense breasts (1). A growing body of evidence shows that women with dense breasts have a moderately increased risk of breast cancer relative to women with fatty breasts (2). Specifically, women with the densest breasts (density above 75%) have 4-6 times higher the chance of getting breast cancer than women with the least dense breasts (3).
The link between breast density, the risk of breast cancer, and the benefits of supplemental screening is currently under investigation in Canada. Sufficient evidence is lacking to advocate for routine additional breast cancer testing among women with dense breasts. Clinically validated data indicating improved screening outcomes for women with dense breasts, and specifically, proof of mortality reduction in randomized trials, is required before new Canadian guidelines surrounding supplemental screening in women with dense breasts are implemented. Research has shown, however, that ultrasound finds small, invasive nodenegative cancers that can be missed on mammograms in women with dense breasts.
5 reasons why breast density matters
- Reduced sensitivity of mammography for early breast cancer detection. Having dense breasts can result in cancer being missed by mammography. This is because both cancer and normal dense breast tissue show up on a mammogram image as white.
- Increased risk for breast cancer. Increased breast density is associated with moderately increased risk of breast cancer. Women with the highest category of density are up to twice as likely to develop cancer as women with average density.
- Increased risk of an interval cancer. Women with extremely dense breasts are more likely to have breast cancer discovered between routine mammogram screenings (when cancer masses are larger and can be felt during a physical breast exam).
- Increased risk of cancer in the opposite breast. Women with dense breasts who have been diagnosed with breast cancer are more likely to develop cancer in the opposite breast.
- Dense breasts are normal and common. About 40% of women over 40 have dense breasts.
What are the implications of having dense breasts as it relates to cancer screening?
It is important to note that women with dense breasts experience reduced sensitivity of mammography to detect early breast cancer. Every woman’s breasts are composed of both fat and breast tissue, but the proportions of each vary from woman to woman. Dense breasts have a higher proportion of breast tissue, whereas fatty breasts have a higher proportion of fat. As it relates to screening mammography, fat tissue appears dark gray or black, whereas breast tissue and cancer both appear white, making the cancer more difficult to spot.
What are the Canadian guidelines surrounding the subject of breast density?
The Canadian Task Force Guidelines on the subject of breast density are due to be updated as it relates to disclosure to women of their breast density, as recorded in a mammogram report. This October, British Columbia became the first province in Canada to provide information about breast density to women and their doctors after their mammogram screening tests. Click here to read the full article.
Speak to your Medisys doctor about your breast density status to understand the best course of action for you, based on your current health status and risk factors.
How is breast density classified?
Scientifically speaking, breast density is a measure of the extent of radiodense fibroglandular tissue in the breast, and the impact of breast density on screening accuracy is a recognized risk factor for breast cancer (4). Several classification systems can be used to distinguish breast density ranging from almost entirely fatty, scattered fibroglanduar tissue, heterogeneously dense, and extremely dense. Commonly, a density of between 50 percent and 100 percent is considered “dense”, whereas a density of 75 percent or more would be considered “extremely dense”.
My breasts are firm. Does that mean they are dense?
Breast density cannot be determined by breast size or by touch. Dense breasts can feel soft, lumpy or firm and so can fatty breasts. Breast density can only be determined on a mammogram.
I’ve already had a mammogram, how do I find out if I have dense breasts?
- In BC, as of October 15, 2018, breast density results appear in mammogram results letters (5).
- In AB, NB, QC, YT, speak with your doctor about what your mammogram results say about your breast density.
- In NS, after receiving a mammogram, women can submit a request to find out their breast density records. Speak with your doctor.
- In ON, SK, NL, PEI, NWT and MB density is recorded as either “less than 75%” or “over 75%” and thus, women in the 50-75% category cannot find out their density based on standard mammogram results letters.
- In ON, SK, NL, PEI, NWT women with >75% density are recalled annually for a mammogram.
I have been diagnosed with dense breasts, what should I do?
If you have been diagnosed with dense breasts and are concerned about your risk of breast cancer, speak to your doctor about your breast density and its potential implications, as well as any additional risk factors you may have for breast cancer. It is recommended that eligible women have regular screening mammograms, as advised by their doctor, because research shows that women who have screening mammograms are 40-44% less likely to die of breast cancer, than women who don’t.
For women with dense breasts, a normal mammogram result may not always be accurate. You and your doctor may wish to consider additional testing such as supplemental ultrasound. Supplemental ultrasound screening in specific situations can lead to earlier detection of breast cancer (eg. identification of cancers that have not yet spread to the lymph nodes); however, supplemental ultrasound screening is not recommended for routine screening in Canada. It is important to note that currently in Canada, screening mammography remains the recommended tool for breast cancer detection and consistently has demonstrated a reduction in breast cancer mortality. Canadian guidelines surrounding the subject of breast density have yet to be established. However, women with elevated risk are encouraged to speak with their doctor if they would like to consider ultrasound for adjunctive screening, after weighing benefits and risks. Speak to your doctor to discuss the best plan of action for you.
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What can I do to reduce my risk?
Some risk factors (like our genetic makeup) are out of our control, but we can all control modifiable risk factors like maintaining a healthy diet, exercising regularly, reducing stress, not smoking, and limiting alcohol consumption to decrease our overall cancer risk and to improve our overall health. Being proactive about your health also includes preventive health screening. Detecting cancer at the earliest possible stage typically results in less invasive treatment and the best health outcomes. It is also important to note that no screening procedure or combination of procedures is 100% effective in detecting all possible health risk issues including all cancers. Click here to learn more about our preventive health services.
Sources: 1. Sprague BL, Gangnon RE, Burt V, et al. Prevalence of mammographically dense breasts in the United States. J Natl Cancer Inst 2014;106(10):10.1093/jnci/dju255. Print 2014 Oct. 2. Harvey JA, Bovbjerg VE. Quantitative assessment of mammographic breast density: Relationship with breast cancer risk. Radiology 2004;230:29-41. 3. Chiu SY, Duffy S, Yen AM, Tab+ír L, Smith RA, Chen HH. Effect of Baseline Breast Density on Breast Cancer Incidence, Stage, Mortality, and Screening Parameters: 25-Year Follow-up of a Swedish Mammographic Screening. Cancer Epidemiology Biomarkers & Prevention 2010;19(5):1219-1228. 4. Ciatto, Visioli, & Zappa, 2004. 5. https://globalnews.ca/news/4476224/bc-breast-density-screening/