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Breast Density

What is breast density?

Breasts come in all sizes and densities. They are composed of “non-dense breast tissue” (otherwise known as fatty tissue) and “dense breast tissue” (comprised of milk glands, ducts and supportive tissue). What determines your breast density is the proportion of dense breast tissue you have; this greatly varies from individual to individual and may change over time. Dense breast tissue is common and is normal.

How is breast density determined?

Breast density can only be seen on a mammogram. It is not related to breast size or firmness. The four categories identified on a mammogram image below are listed in order of increasing density, with a BIRADS A category being the least dense category (mostly fatty tissue) and a BIRADS D category being the most dense (highest proportion of non-fatty tissue). Most women are in the middle two categories.


Why is breast density important?

Dense breasts are associated with an increased risk for the development of breast cancer. However, having dense breasts does not necessarily mean that you will develop breast cancer. Density is one of many recognized risk factors for breast cancer. For instance, increasing age is a risk factor that affects all women.


What should women do if they have dense breasts?

Many cancers are found on mammograms even if dense breast tissue is present. It is important to get a regular mammogram, as this is the only test proven to decrease the risk of death from breast cancer. Other tests such as ultrasound and magnetic resonance imaging (MRI) are under investigation, but there are currently no provincial or national recommendations or guidelines for their use in screening. 

The choice to have additional testing should be made on an individual basis after a
discussion of the risk, benefits and costs with a health care provider.

Women with increased breast density are encouraged to discuss their breast cancer risk with their health care provider. We also encourage all women to review the modifiable risk factors for breast cancer.

BC Cancer’s Breast Screening Program recently commissioned an independent review to evaluate the evidence regarding breast density and breast cancer risk including the scientific literature and BC Cancer Breast Screening Program data. As a result of the review, three recommendations were made to BC Cancer:

  • Develop a plan to communicate breast density results in British Columbia
  • Continuously assess the performance of the Breast Imaging Reporting and Data System (BIRADS) density scoring within BC Cancer’s Breast Screening Program and monitor the scientific literature for opportunities for improvement
  • Monitor ongoing results of randomized controlled trials of supplemental screening in women with mammography
The Breast Screening Program will be enacting all of the recommendations.

Starting mid-October 2018, individual breast density BIRADS score will be included with screening mammography results to all women and their providers and will include information about breast density.

As this is a complex issue, BC Cancer will be forming a working group to implement a comprehensive set of new educational tools and support around breast density for province-wide roll out in January 2019.

The full report is available here
All women in BC, and their care providers, will receive their BIRADS breast density category with their screening mammogram results by as of mid- October 2018.

Women can access their breast density category from previous screening mammography results by request to the Breast Screening Program.

The reasons for differences in breast density between women are unknown. Breast density is common and breasts tend to become less dense as women age. Most women fall in the middle two density categories. BC Cancer Breast Screening Program data showed that 17 per cent of women screened were A, 42 per cent were B, 32 per cent were C and 7 per cent were D. 

BC Cancer Breast Screening Program data are also being studied to better understand any relationship between breast density and ethnicity.
Breast density is a risk factor for developing breast cancer, although having even the highest breast density does not mean that breast cancer is certain. The other risk is that breast density may make it more difficult to find signs of breast cancer on a screening mammogram, which is called “masking.” 

Breast density is not a major cancer risk factor compared with other commonly recognized risk factors. Approximately 10 per cent of women are considered to have extremely dense breasts while about 80 per cent have density in the middle two categories. When compared with women who have density in the middle two categories, the risk for women with extremely dense breasts is about two times greater. 
No, breast density is one of multiple risk factors. Increasing age, for example, is another risk factor and one that affects all women. It is very important to consider breast density in combination with this and other possible factors such as family history of breast cancer or identification of certain genes. The relationship between these factors is not completely understood and remains under investigation.  Discussions with care providers regarding breast density should include other risk factors and possibly the need for a breast cancer risk assessment, regular breast examinations and investigations of any signs or symptoms of breast disease.
Yes, mammography is still the best overall breast cancer screening test for women who are not showing symptoms. It is able to detect many breast cancers before symptoms occur, even in women with the densest breasts. Recent medical evidence, which has also included Canadian screening data, has shown a 40 per cent decrease in death from breast cancer. 

The chance of not detecting a cancer is increased in dense breasts due to the “masking” effect. However, mammography is able to detect some breast cancers more effectively than ultrasound or magnetic resonance imaging (MRI). Regardless of breast density, mammography will not detect all breast cancers. Thus, it is important for women to be aware of the normal look and feel of their breasts, and to bring any breast changes to their health care provider’s attention, even if their last mammogram was normal.  
BC Cancer Breast Screening Program data finds that there is little difference in the likelihood that cancers will be found by annual screening compared to every two years in women who have the densest breasts. However, if a woman has a first degree relative (mother, sister, daughter) diagnosed with breast cancer, then annual screening with mammography is available and recommended.
Screening annually is not recommended for women who are otherwise at average risk. Only women with a first degree relative (mother, sister, daughter) diagnosed with breast cancer are eligible for annual screening mammography. Women with concerns about their breast health should consult with their primary health care provider. 
Supplemental screening (breast ultrasound, breast MRI) of women with dense breasts who are otherwise of average risk is currently not recommended. The review of the medical literature indicates that there is currently not enough evidence to provide additional screening for dense breasts.  At present, no provincial or national program offers this. 

The early evidence does show that breast ultrasound and breast tomosynthesis (also known as 3D mammography) can increase cancer detection in women with dense breasts compared to mammograms alone, but the overall long-term benefits and downsides of supplemental screening are not completely understood at this time.
Breast cancer can occur in women with all levels of density. Mammography is the best overall breast cancer screening test for women with no symptoms. It is able to detect many breast cancers before symptoms occur. However, mammography will not detect all breast cancers. It is important for women to be aware of the normal look and feel of their breasts, and to bring any breast changes to their health care provider’s attention, even if their last mammogram was normal.  
Modification of breast density, including by medication, is being studied, but there are no standardized practices in Canada. Breasts tend to become less dense as women age; however hormone therapy may increase breast density. 

Alterations in diet or weight loss are unlikely to reliably affect breast density, but the latter is one recognized means of decreasing overall breast cancer risk. Others include maintaining an active lifestyle, limiting alcohol intake, breastfeeding, and considering the risks and benefits of hormone therapy for menopause symptoms with the care provider. Learn more about these here.


SOURCE: Breast Density ( )
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