Dense Breasts and Breast Cancer Risk

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Having dense breasts is one of the risk factors associated with breast cancer. Most women do not know whether or not they have dense breasts because this characteristic can't be identified based on appearance or firmness of your breasts. Breast density can only be established with an imaging examination, such as a mammogram.

Because breast density may be a factor in terms of breast cancer risk, it is often noted in mammogram reports. However, that is not always the case.

four categories of breast density
Verywell / Jessica Olah

Characteristics of Dense Breasts

Breasts are composed of fibrous, glandular, and fatty tissue. A woman's breasts are considered dense if they have less fat and more glandular and fibrous tissue than average.

There are four categories used to describe breast density:

  1. Breasts that are the least dense have almost all fatty tissue
  2. Breasts that have scattered areas of fibroglandular density
  3. Breasts with heterogeneous density
  4. Breasts that have almost all glandular and fibrous tissue with little to no fatty tissue.

Dense breasts are more common among women who are young (premenopausal) and postmenopausal women who take hormone therapy for symptoms of menopause.

Impact on Breast Cancer Risk

Dense breasts are associated with an increased risk of breast cancer. And the denser a woman's breasts are, the higher the risk of breast cancer. The reason for this association is not completely clear.

To give a sense of perspective about the increased risk of breast cancer with dense breasts:

  • Oral contraceptives increase the risk of breast cancer by 1.3 times
  • Heterogenous breasts increase the risk by 1.6
  • Extremely dense breasts increase the risk by 2.04
  • A first-degree relative with breast cancer diagnosed before age 40 increases the risk by 3.0

The Breast Cancer Surveillance Consortium (BCSC) Risk Calculator is a tool used to asses five- and 10-year breast cancer risk based on age, race/ethnicity, family history of breast cancer, history of a benign breast biopsy, and breast density. While part of this calculation, dense breasts are not the strongest risk factor.

A previous personal history of breast cancer, a family history of breast cancer, having a genetic mutation associated with breast cancer, and possibly smoking are all bigger risk factors for breast cancer than dense breasts are.

Accuracy of Mammograms

The increased risk of breast cancer in dense breasts is particularly concerning because dense breast tissue can lead to false-negative mammograms—that is, a missed diagnosis.

Dense breasts are characterized by white areas on a mammogram—but so is breast cancer. Tumors can be obscured or blend in with dense breast tissue, which is why interpretation of a mammogram can be challenging in women with dense breasts.

However, mammograms are considered the screening tool of choice for women who have dense breasts because they can still identify most breast cancers, and they are believed to have more accuracy than other diagnostic tests.

Next Steps

For women who have dense breasts, the combination of mammography and breast ultrasound may increase the detection of breast cancer (but with more false positives).

Fast MRI

Studies suggest that adding fast breast magnetic resonance imaging (MRI) to mammography is more likely to detect breast cancers, especially aggressive ones.

While conventional breast MRI is the most sensitive measure to detect the disease, it is very costly relative to mammography and is currently only recommended for people who have a high lifetime risk of developing breast cancer.

Unlike mammography, the accuracy of MRI is not altered by dense breasts.

Fortunately, fast breast MRI is a newer procedure that takes only around 10 minutes to perform and significantly increases the chance of finding a breast cancer that is present.

With regard to cost, it is comparable to the cost of mammography, thus offering an option for women who have an elevated risk of breast cancer due to having dense breasts but who do not meet the criteria for conventional breast MRI screening.

Since fast MRI is relatively new, not all radiology departments are equipped to do this screening.

Breast Density Reporting

Concern over the increased risk for breast cancer in women with dense breasts has resulted in some states adopting legislation that mandates doctors to inform women if they have dense breasts, and to discuss additional imaging options following a normal mammogram.

In states where written notifications are the law, mammogram reports must include specific notification about breast cancer density, such as:

Your mammogram shows that your breast tissue is dense. Dense breast tissue is very common and is not abnormal. However, dense breast tissue can make it harder to find cancer on a mammogram and may also be associated with an increased risk of breast cancer. Use this information to talk with your doctor about your risks for breast cancer. At that time, ask your doctor if more screening tests might be useful, based on your risk. A report on your results was sent to your physician.

Congress is currently considering enacting similar legislation that would require this type of language in all states.

The U.S. Food and Drug Administration (FDA) has also put forth a proposal that would require that mammogram reports include an assessment of breast density along with language that explains the impact of breast density on the accuracy of the report and on the risk of breast cancer.

A Word From Verywell

If you have been told that you have dense breasts, the best course of action is to meet with your doctor to discuss your medical history and other factors that might increase your overall risk for breast cancer. You may need additional imaging with breast ultrasound or breast MRI, or genetic testing, or you might be advised to continue your yearly screening mammograms.

Be sure to do your monthly breast self-examinations and to be attentive to changes in your breasts, such as nipple changes and pain.

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