Dense Breasts: Are You Educated?

By Wendie A. Berg, MD, PhD, FACR

What are Dense Breasts?

The normal appearance of breasts, both visually and on mammography, varies greatly. On mammography, one of the important ways breasts differ is in their density.

All breasts are made up of fatty tissue as well as glandular and fibrous connective tissue. The ratio of fatty tissue to the other tissues, however, varies from woman to woman, and breast to breast. Some breasts are mostly fatty and some breasts are mostly dense, with the majority in the middle. Breasts made up mostly of glandular rather than fatty tissue are classified as “dense breasts.” The way breasts look and feel does not predict whether or not they are dense on mammography. Radiologists describe breast density using specific language:

A. almost entirely fatty;
B. scattered fibroglandular tissue;
C. heterogeneously dense, which can obscure detection of small masses; and
D. extremely dense which lowers the sensitivity of mammography (see Figure 1).

The last two categories are considered “dense.” About 40% of women over the age of 40 have dense breasts.¹

Figure-1 — Figure 1 (click for full size). On mammography, there is a wide range of normal patterns of breast density, from A) fatty, to B) scattered fibroglandular tissue, to C) heterogeneously dense, to D) extremely dense. Categories C and D are considered “dense.” As breast density increases, so does the likelihood that cancer, if present, can be masked by normal tissue and not detected on mammography. (Courtesy Dr. Wendie Berg)

Why does breast density matter?

A mammogram is essentially an x-ray of the breast, and x-rays have difficulty penetrating dense breast tissue. Dense breast tissue shows up as white areas on a mammogram. Cancerous masses are also dense and white and can therefore be hidden by normal dense tissue (though malignant calcifications are well seen on mammography across all breast densities). In any woman, cancer may be found because of a lump after a normal mammogram, but this is much more likely to occur in a woman with dense breasts (see Figure 2).²

Figure 2. Mammograms from this 46-year-old woman appear normal with heterogeneously dense tissue. Four months later, the woman noted a right breast lump. On ultrasound directed to the lump, an irregular mass (arrow) was identified that is highly suggestive of cancer. Ultrasound-guided core needle biopsy showed aggressive invasive ductal cancer which was not seen even in retrospect on the mammogram. (Courtesy Dr. Wendie Berg)

How does a woman know she has dense breasts?

Breast density is determined with mammography and can also be recognized on CT scans or MRI. Until recently, it has not been a requirement that the results letter a woman is sent after her mammogram include information about breast density, though breast density has been recommended to be included in the report to the doctor for decades. Laws have now been enacted in 27 states that require some information about breast density be communicated in the results sent directly to patients. Click here for a list of states with density inform laws and specifics of each state requirement.

What should I be telling my patients?

Dense breasts are normal, and there is no need to panic. Women with dense breasts, however, are more likely to develop breast cancer and are more likely to have that cancer missed by a mammogram [though a digital mammogram is better than film].^3,4 Tomosynthesis (3D mammography) adds detection of 1-2 cancers per 1000 women screened compared to standard 2D mammography, and this increase in cancer detection is observed across all breast densities.^5,6 Ultrasound, when added to mammography in women with dense breasts, adds detection of 2-4 early stage invasive cancers per 1000 women screened.^7-9 The only study to date comparing ultrasound with tomosynthesis showed nearly twice as many additional cancers were seen on ultrasound as on tomosynthesis after a negative standard mammogram.¹⁰ MRI shows even more cancers than the combination of mammography and ultrasound.^8,11-13 All screening can result in false positives – abnormalities that are not cancer but that require follow-up or a needle biopsy. Women determined to be at “high risk” for breast cancer due to genetic/family history or other risk factors are recommended to have an MRI as part of their annual screening.¹⁴ Click here for a screening decision support flow chart, “Who Needs More Screening?”

If a woman has dense breasts, it is particularly important for her to be aware of how her breasts normally feel and to report any changes to her healthcare provider. It is also important that a woman discuss all of her risk factors, including breast density, with a healthcare professional. A helpful tool is the Patient Risk Factor Checklist which can be downloaded and printed.

Despite growing awareness of breast density, there has been little educational information on what it means and what to do about it. Together with JoAnn Pushkin, a patient advocate, and Cindy Henke-Sarmento, a technologist, we have developed a medically sourced website to help women and their healthcare providers become educated about breast density and screening options. For more information about dense breasts, patient question and answers and screening options, please visit: http://www.DenseBreast-info.org. We will also be exhibiting at the upcoming AHRA Annual Meeting in Nashville. Please stop by our booth (#222) for more information!

References:

1. Sprague BL, Gangnon RE, Burt V, et al. Prevalence of mammographically dense breasts in the United States. J Natl Cancer Inst. 2014;106.
2. Mandelson MT, Oestreicher N, Porter PL, et al. Breast density as a predictor of mammographic detection: comparison of interval- and screen-detected cancers. J Natl Cancer Inst. 2000;92:1081-1087.
3. Nelson HD, Zakher B, Cantor A, et al. Risk Factors for Breast Cancer for Women Aged 40 to 49 Years: A Systematic Review and Meta-analysis. Ann Intern Med. 2012;156:635-648.
4. Pisano ED, Gatsonis C, Hendrick E, et al. Diagnostic performance of digital versus film mammography for breast-cancer screening. N Engl J Med. 2005;353:1773-1783.
5. Friedewald SM, Rafferty EA, Rose SL, et al. Breast cancer screening using tomosynthesis in combination with digital mammography. JAMA. 2014;311:2499-2507.
6. Skaane P, Bandos AI, Gullien R, et al. Comparison of Digital Mammography Alone and Digital Mammography Plus Tomosynthesis in a Population-based Screening Program. Radiology. 2013;267:47-56.
7. Berg WA, Mendelson EB. Technologist-performed handheld screening breast US imaging: how is it performed and what are the outcomes to date? Radiology. 2014;272:12-27.
8. Berg WA, Zhang Z, Lehrer D, et al. Detection of breast cancer with addition of annual screening ultrasound or a single screening MRI to mammography in women with elevated breast cancer risk. JAMA. 2012;307:1394-1404.
9. Brem RF, Tabar L, Duffy SW, et al. Assessing Improvement in Detection of Breast Cancer with Three-dimensional Automated Breast US in Women with Dense Breast Tissue: The SomoInsight Study. Radiology. 2015;274:663-673.
10. Tagliafico AS, Calabrese M, Mariscotti G, et al. Adjunct screening with tomosynthesis or ultrasound in mammography-negative dense breasts (ASTOUND): Interim report of a prospective comparative trial. J Clin Oncol. March 9, 2016; [Epub ahead of print].
11. Kuhl C, Weigel S, Schrading S, et al. Prospective multicenter cohort study to refine management recommendations for women at elevated familial risk of breast cancer: the EVA trial. J Clin Oncol. 2010;28:1450-1457.
12. Sardanelli F, Podo F, Santoro F, et al. Multicenter surveillance of women at high genetic breast cancer risk using mammography, ultrasonography, and contrast-enhanced magnetic resonance imaging (the high breast cancer risk Italian 1 study): final results. Invest Radiol. 2011;46:94-105.
13. Warner E, Plewes DB, Hill KA, et al. Surveillance of BRCA1 and BRCA2 mutation carriers with magnetic resonance imaging, ultrasound, mammography, and clinical breast examination. Jama. 2004;292:1317-1325.
14. Saslow D, Boetes C, Burke W, et al. American Cancer Society guidelines for breast screening with MRI as an adjunct to mammography. CA Cancer J Clin. 2007;57:75-89.

Wendie A. Berg, MD, PhD, FACR is a professor of radiology at Magee-Womens Hospital of University of Pittsburgh School of Medicine in Pittsburgh, PA. She can be reached at wendieberg@gmail.com.