Is breast cancer risk increased if you have dense breasts?

breast cancer

It can be unsettling for any woman reading her mammogram report and seeing a phrase saying “dense breast tissue” within the findings. What does this mean in regards to her breast cancer risk?

First, there’s no need to panic as it does not mean you have breast cancer. Instead, the results are informing you that, like 40 percent of other American women, your breast tissue is particularly fibrous.  However, dense breast tissue also makes it more difficult for a radiologist, a medical doctor who interprets imaging tests to diagnose if a person may have breast cancer or not, to see through the entire breast which could possibly increase the risk of breast cancer.

What causes dense breast tissue?

It is not entirely understood why some women have more dense breasts than others. But, here are a few reasons that may increase this possibility:

  • Younger age: Breast tissue tends to become less dense with age. However, some women may have dense breast tissue at any age.
  • Lower body mass index: Women with less body fat are more likely to have more dense breast tissue compared to women who are obese.
  • Using hormonal therapy for menopause: Women who take combination hormone therapy to relieve signs and symptoms of menopause are more likely to have dense breasts.

What does this mean for women with dense breasts?  

To understand what the term dense breasts means, it helps to have an understanding of the make-up of breast tissue.  Breasts are mainly made up of four kinds of tissue:

  1. Breast lobules – The breast is made up of glands called lobules that can make milk.
  2. Breast ducts – These are ducts that carry milk to the nipples.
  3. Fibrous tissue – Fibrous breast tissue includes ligaments, supportive tissues, and scar tissue.
  4. Fat – Breasts will have a layer of fatty tissue surrounding the breast glands which extends throughout the breast. The fatty tissue gives the breast a soft consistency.

Large breasts are different from small breasts in that large breasts have more fat tissue than small breasts.  In young, premenopausal women, hormones keep the lobules and the ducts active with the ups and downs of the hormones which can increase the fibrous tissue.  If a woman gains weight, this can increase the amount of fat tissue while weight loss can reduce the amount of fat within the breast.

When a woman has a mammogram, the x-rays easily go through fat tissue but do not go through fibrous tissue very well.  These same x-rays also do not go through a cancerous lump within the breast very well either.  Breast tissue that is fibrous along with ductal tissue look white on a mammogram just like a cancerous lump does – fatty breast tissue appears dark making it easier to read.

About two-thirds of women under the age of 50, or premenopausal, often have dense breasts as noted by the mammogram.  As a woman ages, only about one-quarter will still have dense breasts.  Aging and weight gain can lead to the breasts becoming mostly fat.  The fattier the breasts, the easier they are to read by a radiologist to on a mammogram, making it easier to detect breast cancer.

Fatty breasts are easy to read for breast cancer but dense breasts are harder to read, particularly if there is a small cancerous lump that could be missed.

Breast density classified into four groups

The Breast Imaging Reporting and Database Systems, or BI-RADS, which reports findings of mammograms, also includes an assessment of breast density.  BI-RADS classify breast density into four groups:

  • Mostly fatty – The breasts are made up of fat and contain little fibrous and glandular tissue. This means the mammogram would likely show anything that was abnormal.
  • Scattered density – The breasts have quite a bit of fat, but there are a few area of fibrous and glandular tissue.
  • Consistent density – The breasts have many areas of fibrous and glandular tissue that are evenly distributed through the breasts. This can make it hard to see small masses in the breast.
  • Extremely dense – The breast have a lot of fibrous and glandular tissue. This may make it hard to see cancer on a mammogram because the cancer can blend in with the normal tissue.

Are women with dense breasts more vulnerable to developing breast cancer?

There are conflicting reports on whether women with dense breast actually are at a higher risk or not.  Keep in mind the fact that because of the breast’s density, it simply is more difficult for a radiologist to read a mammogram and therefore a cancerous lump could be missed.  But the National Cancer Institute has found that women with extremely dense breasts also have the highest breast cancer rates.  This finding is in line with other studies that have come that the same conclusion. A 2017 study attributed the increased risk of breast cancer in women with dense breasts to the high cellular content of dense tissue and interaction between cells that line the mammary ducts and surrounding tissue.

Research has not found the specific biological link between breast density and breast cancer but some studies point to hormones as being a factor, especially the use of synthetic hormone replacement therapy (HRT).  A 2010 joint study stated “Postmenopausal women with high breast density are at an increased risk of breast cancer and should be aware of the added risk of taking hormone therapy, especially estrogen plus progestin.”  Basically the study found that of the over 500,000 women screened, the breast cancer risk was 3 times higher for post-menopausal women with extremely dense breasts who were also taking synthetic hormone replacement therapy.

If you are a woman who has extremely dense breasts, it does not mean that breast cancer is inevitable.  It does that your risk may be slightly higher.

At this time, there are no specific recommendations on lowering breast cancer risk for women with dense breasts.  However, all women can take steps to lower their breast cancer risk by making healthy lifestyle choices.

All women should know what level of density their breasts are composed of.  If you are a woman with dense breasts, discuss with your doctor which breast cancer screening tests are right for you.

Is breast cancer risk increased if you have dense breasts?
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Dr. David Samadi

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Dr. David Samadi