Understanding Breast Density

One size doesn’t fit all

Are you aware of your breast density? It’s up to each woman to be educated when it comes to breast density and risk. Understanding will enable you to receive the personalised screening you need.

Breast Density 101

1. What is breast density?

Breasts are made up of three types of tissue – fatty, fibrous and glandular tissue. Every woman is unique and has a different amount of these three types of tissue. A person with dense breasts (on a mammogram) has less fatty tissue and more glandular and fibrous tissue.1

As you can see from the mammogram images below, some breasts are mostly made up of fatty tissue. Others are mostly made up of glandular and fibrous tissue, and these are known as dense breasts.

2. Why is breast density important?

Women with dense breasts (on mammogram) have a four to five times increased risk of breast cancer compared with women with low breast density.2,3 It is currently unclear as to why this is, so more research is needed in this field.2 There is also an increased risk of breast cancer not being detected by a standard mammogram in women with dense breasts.4,5 As you can see in the image below, dense breast tissue appears whiter on a mammogram image. This makes it more difficult for radiologists to interpret and often results in the need for additional imaging.1

3. Why does high breast density hide cancers?

Dense breast tissue appears whiter on a mammogram image, making it more difficult for radiologists to interpret and often resulting in the need for additional imaging.1 Imagine dense breast tissue as clouds in the sky and breast cancers as white planes in flight. When a plane flies through wispy clouds, you can still see the plane in the air, but when a plane flies through thick clouds, it can be nearly impossible to visually detect.

4. How common are dense breasts?

We’ve all heard of high risk breast cancer gene mutations, such as BRCA1 and BRCA2, that occur in 5–10% of all breast cancers.2 But did you know that having dense breasts is a far more common risk factor for breast cancer?6 While it is not known exactly how many women in Australia have dense breasts, international studies suggests that dense breasts occur in more than half of women aged under 50 years, in around 40% of women in their fifties and in about 25% of women aged 60 and older.6 So as you can see, breast density is very common and is not abnormal.1

5. What is Australia doing in regards to breast density?

In the USA, 28 (56%) states have adopted a mandatory breast density notification requirement since 2005 and Federal legislation is pending.7,8 However, in Australia, there is currently no requirement for breast density to be provided on mammogram reports.6 That means that it is up to you and your doctor to ask that this information be included in your mammogram report. You and your doctor can then use this information to help plan a breast cancer screening approach that is most suited to your individual needs.

6. Why are standard mammograms less accurate in women with dense breasts?

Standard 2D digital mammography is currently the most common screening method used in Australia. However, it does have some limitations. Standard mammograms may be less accurate in women with dense breasts because dense breast tissue appears more opaque on a mammogram, making it harder for doctors to spot any abnormalities or cancers on the scan, as these also appear opaque on a mammogram.9

References: 1. American Cancer Society. Available at: https://www.cancer.org/cancer/breast-cancer/risk-and-prevention/breast-cancer-risk-factors-you-cannot-change.html. Accessed November 2017. 2. Boyd NF et al. N Engl J Med 2007;356:227–36.
3. Yaghjyan L et al. J Natl Cancer Inst 2011;103:1179–89. 4. Skaane Pet al. Radiology 2013;267:47–56. 5. Ciatto S et al. Lancet Oncol 2013;14:583–9. 6. BreastScreen SA. Breast density Information for consumers. Available at: http://www.sahealth.sa.gov.au/wps/wcm/connect/6e1a80804e78310ebd28fdc09343dd7f/Breast+Density+Consumer+Information v3_FORMATTED.pdf?MOD=AJPERES&CACHEID=6e1a80804e78310ebd28fdc09343dd7f.  Accessed November 2017.
7. American College of Radiology. Available at: https://www.acr.org/Advocacy/eNews/20170217-Issue/20170217-StateBreast-Density-Reporting-Laws-Proliferate. Accessed September 2017. 8. Freer PE. Radiographics 2015;35:302–15.  9. Breast Cancer Network Australia. Available at: https://www.bcna.org.au/about-us/advocacy/position-statements/family-history-and-hereditary-breast-cancer/. Accessed November 2017.

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