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Breast Density Movement

We’ve Come So Far, But Still Have Far To Go!

By Dr. Paula Gordon

The breast density movement in the US started in 2004 with Dr. Nancy Capello. As of early 2021, 37 states and the District of Columbia have legislation requiring women to receive some information about breast density. And soon, ALL women in the USA will be informed.

We started our advocacy 12 years later in Canada, but have had great success so far.

Kathy Kaufield of Saint John found her breast cancer by chance. While on a business trip in 2015, she didn’t have the shower puff she regularly used in the shower at home. When her soapy hand grazed the underside of her left breast, she felt a lump. She thought it couldn’t be cancer. After all, she just had a negative mammogram five months earlier.

Kathy didn’t know she had dense breasts, and she didn’t know the implications of dense breasts. She wasn’t aware that she shouldn’t trust her mammogram as much as she had. Unfortunately, like many women, she didn’t know she should have been more vigilant with her monthly breast self-exams.

Following surgery, 16 rounds of chemotherapy, and six weeks of radiation, Kathy became an advocate for breast density notification. She joined other patient advocates including Dense Breasts Canada, and since its beginnings in 2016, women in Kathy’s province of New Brunswick and 5 other provinces in Canada are now notified of their breast density in their screening mammogram results letter.

What is breast density?

Every woman’s breasts are composed of fat and breast tissue, but the proportions vary. There are four categories of breast density. Categories C and D are considered “dense.” Dense breasts are normal. Over 40 per cent of women aged 40+ have dense breasts. Approximately 40 per cent of women have heterogeneously dense breasts (Category C) while 10 per cent have extremely dense breasts (Category D).

How is breast density determined?

Breast density is determined only on a mammogram. It cannot be determined through physical examination. Most commonly, breast density is determined by a radiologist when they look at the mammogram. Software that can determine density is being incorporated into mammography equipment, but it is not yet widely used in Canada.

Why does breast density matter?

Dense breasts reduce the accuracy of a mammogram. A missed diagnosis like Kathy’s is more likely with dense breasts because dense breast tissue and cancer both appear white on mammograms, so cancer can be masked. Mammograms are 92-100 per cent effective in fatty breasts but only 50 per cent effective in the highest density.

Dense breasts are an independent risk factor for breast cancer. The denser the breasts, the higher the risk. Cancer occurs four to six times more often in women with the highest level of density than in women with the lowest level. Breast density is a more prevalent risk factor than family history.

Dense breasts result in higher rates of interval cancers. As seen in Kathy’s case, women with dense breasts may find a lump after a negative mammogram. These are called “Interval cancers” are 18 times more common in women with dense breasts. Interval cancers are larger at diagnosis and more often node-positive and more aggressive subtypes. They are more likely to need more aggressive treatment and are more likely to require mastectomy, axillary dissection and chemotherapy. They have a poorer prognosis compared to screen-detected cancers.

What should physicians discuss with women who have dense breasts:

  • any other risk factors the patient may have; breast density should be placed in context with other risk factors and risk reduction strategies;

  • the importance of having regular mammograms and consideration of annual mammograms for Category C and D;

  • the importance of regular self-exams;

  • modification (improving) of lifestyle behaviours: maintaining a healthy weight, increasing exercise, decreasing alcohol intake and avoiding/decreasing hormone use.

Evidence of benefits of supplemental screening for women with dense breasts

Mammography is the only screening test proven to reduce deaths due to breast cancer because it is the only modality studied in an RCT. The key to mortality reduction by screening is finding cancers smaller, and before they have spread to the lymph nodes, and reducing the incidence of advanced cancers. It has been known since 1995 that ultrasound can find cancers in dense breasts that were missed on mammograms. Subsequent research from multiple institutions confirms that ultrasound can find 3-4 cancers per 1,000 women screened. An RCT of supplementary ultrasound screening is underway in Japan and is showing greater cancer detection and reduced interval cancers.

The Canadian Association of Radiologists’ position paper states, “supplemental screening breast ultrasound may be considered for patients with dense breast tissue (C & D density categories),” and annual mammography is suggested for all women with extremely dense breast tissue (Category D).

False alarms occur with screening ultrasound, just as with mammograms and pap smears. These, understandably cause anxiety. Most women are willing to accept the transient stress associated with a recall or even a needle biopsy in exchange for avoiding an advanced cancer diagnosis.

Physicians have a key role to play by considering breast density in context of other risk factors, assessing a woman’s overall risk, identifying higher-than-average risk patients who need increased surveillance (i.e. Ultrasound and MRI), discussing supplemental screening benefits and harms, and encouraging women to do regular breast self-examination and reduce their modifiable risk factors.

An excellent reference of medically sourced information is

So what’s next:

1. There are another 4 provinces and 3 territories yet to give breast density information directly to women.

2. Supplemental screening should be covered by public health insurance, just like mammography.

3. All women in Canada should be able to access screening mammography starting at age 40. Currently, only 3 provinces’ mammography screening programs allow women to self-refer starting at 40.


Dr. Paula Gordon is a clinical professor in the Department of Radiology at the University of British Columbia. She is a volunteer advisor to both Dense Breasts Canada, a Canadian patient advocacy group, and Dense Breast Info, an American educational website. In recognition of her research and teaching, she has been awarded the Order of British Columbia.

Jennie Dale is a breast cancer survivor, and co-founder of Dense Breasts Canada.


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