Dense Breast Tissue: Your Common Questions Answered

You are relieved to receive the results letter from your screening mammogram stating that there is no evidence of cancer.  However, the relief is short-lived when you read the additional letter included with the mammogram results stating “Your mammogram indicates that you have dense breast tissue…”  Before you become overly concerned,  I would like to discuss 6 commonly asked questions in regards to the dense breast tissue notification legislation.

Once you have a better understanding of breast density and the reasons behind the dense breast tissue notification legislation, my hope is that you, along with your primary care physician, may be able to make a more educated decision regarding your breast cancer screening options in the future.

What is dense breast tissue?

There are two types of breast tissue that make up the breast: fatty tissue and glandular tissue (I also discuss breast tissue in this article).   Fatty tissue is dark on the mammogram.  Glandular tissue is white or grey on the mammogram.  Breast density is subjectively determined by the radiologist’s “eyeball” estimate of the percentage of glandular tissue with respect to the fatty tissue on the screening mammogram.  If there is an equal or greater amount of glandular tissue in the breast compared to the fatty tissue, this is considered “dense breast tissue”.

Approximately 50% of the female population is considered to have dense breast tissue.  The breast radiologist will categorize the breast density for each screening mammogram into one of 4 breast density categories (see image).  If you read your mammogram report, the breast density category should be stated.  The two categories that qualify as dense breast tissue are “heterogeneously dense” and “extremely dense”.

Dense breast tissue categorized by a screening mammogram does NOT correlate with breast firmness as determined by physical exam.

I read my mammogram report, and I have dense breast tissue.  Why did I not receive a dense breast tissue notification letter?

As of March 2016, legislation has been passed in 24 states requiring that women be informed of their dense breast tissue status as determined by the radiologist from a screening mammogram.  Currently, laws vary from state to state concerning how the patient is notified, and what is included in the notification letter.  Given this variability, federal legislation is currently being considered to standardize the notification law across the states.  Nancy M. Cappello, Ph.D. began the grassroots effort to inform and educate women regarding their breast density status after being diagnosed with breast cancer which was not visible on her screening mammogram due to her dense breast tissue.  A few of the goals Dr. Cappello has established with areyoudense.org are to educate the public about dense breast tissue and advocate for change in public policy.

Why did I receive a dense breast tissue notification letter last year, but not this year?

Given the subjective nature of breast density determination, it is not surprising if a woman may receive a dense breast tissue notification letter one year, but not receive the letter the next year.  Designation of breast density does vary between radiologists, and may even vary from year to year with the same radiologist.

Why do I need to know my breast density status?

First, the more glandular tissue in the breast (white on the mammogram), the higher chance of developing cancer (also white on the image) may be obscured, or masked, by the glandular tissue.  Studies have shown that radiologists may not see 15-20% of cancers on a 2D digital screening mammogram. The more glandular tissue present in the breast, the more difficult it may be for the radiologist to see cancer. (RadioGraphics 2015 35:2, 302-315)  Because of this, additional breast cancer screening tests may be warranted in women with dense breast tissue (see #5 and #6 below).

Second, increased breast density (particularly extremely dense breast tissue) is considered an independent risk factor for breast cancer.  Although the degree of increased risk is highly debated, it is generally agreed that this risk is less than the major risk factors of age, family history, reproductive history, and genetic mutations.

The letter encourages me to discuss with my primary care physician if additional screening options are necessary. What are my options?

Before I describe the alternate options for breast cancer screening, it is important to understand that only a fraction of the states required to notify women of their dense breast tissue status also have legislation that mandates insurance coverage for supplemental screenings.  What does this mean?  You might decide with your physician that you should pursue additional breast imaging screening.  However, your insurance company may not pay for it.

That being said, there are multiple options for additional screening (as discussed by Phoebe E. Freer, MD in RadioGraphics 2015 35:2, 302-315).  Please remember, no screening test is 100% able to find cancer, and each screening test has its pros and cons.

• 3D- digital tomosynthesis.

  • Positive: 1-3 MORE cancers detected per 1000 patients compared with digital 2D mammography.
  • Positive: Fewer callbacks for additional imaging compared with 2D mammography because the 3D technology of tomosynthesis enables the radiologist to more accurately differentiate between dense breast tissue and a developing cancer.
  • Negative: Depending on how the images are obtained, the radiation exposure may be higher than a standard 2D mammogram, however still well within the limits set forth by the FDA.

• Whole breast ultrasound.

  • Positive: 2-3 MORE cancers detected per 1000 patients compared with digital 2D mammography.
  • Negative: A woman is 2 times more likely to be asked to return for additional imaging or a biopsy. Many of these women will end up not having cancer (false positive).
  • Performed by an ultrasound technologist or radiologist.
    • Success of this imaging study is dependent on the training and expertise of the technologist performing the study. Because of the variability in training, screening whole breast ultrasound is not offered at many facilities.
  • Automated whole breast ultrasound (ABUS).
    • Approved by the FDA in 2012.
    • Imaging is automatic which will reduce operator error.
    • Unfortunately, this requires the purchase of new equipment, and is also not available at many facilities across the country.

• Breast MRI.

  • Positive: 8 MORE cancers detected per 1000 patients compared with 2D mammography.
  • Negative: A woman is 4 times more likely to be asked to return for additional imaging or a biopsy.  Many of these women will end up not having cancer (false positive).

I understand the different options for additional breast cancer screening, but do I need to undergo additional breast screening?

No single breast imaging screening tool is perfect.  Based on recommendations by the American College of Radiology, Society of Breast Imaging, and the current data on tomosynthesis, I advocate the following additional screening guidelines for women with dense breast tissue in my practice.  However, always consult your primary care physician after receiving a dense breast tissue notification letter to make a final decision.

• Average or low risk for developing breast cancer (lifetime risk of <15% as determined by your physician)
  • Supplemental screening with MRI or whole breast ultrasound IS NOT indicated.
    • If 3D tomosynthesis is offered in your area, consider annual screening with 3D tomosynthesis.
• Intermediate risk for developing breast cancer (lifetime risk of 15-20% as determined by your physician)
  • Supplemental screening with whole breast ultrasound or MRI should be considered after discussion with your primary care physician. The benefits of potentially finding cancer should be weighed against the risk of false positive results (biopsies for non-cancerous lesions).
  • If 3D tomosynthesis was performed for initial screening, this may be considered adequate in intermediate-risk patients.

• High risk for developing breast cancer (lifetime risk of >20% as determined by your physician)
  • Supplemental screening IS recommended.

The dense breast tissue notification law has resulted in confusion among women and primary care physicians.  However, understanding what breast density is, how it is determined, as well as your individual risk for developing breast cancer, will allow you along with your physician to make an educated choice concerning supplemental breast screening.

Written by Danielle Carroll, M.D.

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