Breast density and breast cancer risk

breast density

In Michigan, a new law went into effect on June 1 requiring that mammography service providers inform patients if they have dense breast tissue on screening mammography. Michigan is the 23rd state to enact a law like this. So what exactly is breast density and what does it mean if you have dense breasts?

We talked to Renee Pinsky, M.D., an assistant professor of radiology at the University of Michigan whose specialty is breast imaging. Dr. Pinsky was involved in helping to shape Michigan’s dense breast notification law.

mCancerPartner: What do we mean when we talk about breast density?

Dr. Pinsky: Breast density is determined on a mammogram image. It describes the relative amounts of fat versus fibrous and glandular tissue in the breast. The fat appears as dark or black and the fibrous and glandular tissues appear as white. A mammogram with more white than black is described as dense. The problem arises because cancers appear white on a mammogram. It is difficult to discern a white cancer from the background white tissue in a dense breast.

mCancerPartner: Does breast density change as you age?

Dr. Pinsky: Yes, the general trend is to become less dense with age; however, this is not the case for all women. Factors that can negate the natural tendency to become less dense include taking hormone replacement therapy, as well as weight loss (which would decrease the relative amount of fat or less-dense tissue). Earlier in life, pregnancy and lactation also increase breast density. Weight gain and the medication tamoxifen are known to decrease breast density.

mCancerPartner: Outside of a mammogram, is there any way to know if you have dense breasts?

Dr. Pinsky: Breast density, as it is described today, is an assessment made on a mammogram. You cannot determine your breast density by the way the breasts look or feel. It is not standardized for other imaging techniques.

mCancerPartner: What is the concern over dense breasts that drove this new legislation?

Dr. Pinsky: The new legislation requires that radiologists notify patients of their breast density after their mammogram is performed, along with their mammogram results. The concern over dense breasts is twofold. First, there is the issue of masking, where a cancer that appears white could be hidden in a very dense, white background. A cancer is easier to detect against a fatty or non-dense background. The second issue regarding breast density is that women with dense breasts have a slightly increased risk of breast cancer compared to women with less dense breasts.

mCancerPartner: So, someone with dense breasts has a higher risk of breast cancer?

Dr. Pinsky: Yes, women with heterogeneously dense breasts or extremely dense breasts, which are the two highest categories of breast density, are at slightly increased risk of breast cancer compared to women with less-dense breasts. This has been described in different ways. Women who have extremely dense breasts have a relative risk of breast cancer that’s approximately 2.1 times the risk of women with average breast density. When comparing women who have heterogeneously dense breasts with women with average breast density the risk of breast cancer is approximately 1.2 times. It is recommended that this increased relative risk be part of the discussion to assess the need for additional screening or risk reduction intervention.

mCancerPartner: What screening options are available for women who have dense breasts?

Dr. Pinsky: It is recommended that women of screening age follow the Michigan Cancer Consortium screening guidelines for annual mammography after the age of 40 regardless of their breast density. If tomosynthesis is available, it is recommended as well.

Some women who have dense breasts will need additional screening if they have other risk factors that place them in a high-risk category such as:

  • greater than 20% lifetime risk for breast cancer
  • history of genetic mutations such as BRCA1 or BRCA2
  • untested first degree relative of a BRCA1 or BRCA2 mutation carrier
  • history of thoracic radiation prior to age 30

For these women, we recommend supplemental annual MRI screening in addition to their annual mammogram after the age of 30. Women ages 25-30 should have just MRI.

There’s also an intermediate-risk range in which women with dense breasts should discuss supplemental screening with their clinician. These risk factors include:

  • approximately 15-20% lifetime risk or strong family history of breast cancer
  • prior history of breast cancer
  • prior history of a biopsy with LCIS or atypia

Additional screening options include screening breast ultrasound, screening MRI and in some institutions, screening molecular breast imaging.

Take the next step:

Continue reading about breast cancer risks and what to do if faced with a breast cancer diagnosis:

Renee PinskyRenee Wayne Pinsky, M.D., is an assistant professor of radiology and director of medical student education for breast imaging at the University of Michigan Medical School. She specializes in breast imaging, conducting mammograms and other screening and diagnostic tests at the U-M Comprehensive Cancer Center.



Cancer-center-informal-vertical-sig-150x150The University of Michigan Comprehensive Cancer Center’s 1,000 doctors, nurses, care givers and researchers are united by one thought: to deliver the highest quality, compassionate care while working to conquer cancer through innovation and collaboration. The center is among the top-ranked national cancer programs, and #1 in Michigan according to U.S. News & World Report. Our multidisciplinary clinics offer one-stop access to teams of specialists for personalized treatment plans, part of the ideal patient care experience. Patients also benefit through access to promising new cancer therapies.