From the Editor

Why is breast density a weighty matter?

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What will you tell your patient who asks about the clinical significance of dense breasts detected on her mammogram? Here I offer my current clinical recommendation.



Dense breasts are composed of a lot of fibrous and glandular tissue, with less adipose tissue. Heterogeneously dense and extremely dense breast tissue (as illustrated here) make it difficult to detect breast cancer on mammography, and women with dense breasts have an increased risk of breast cancer.

Case: Patient seeks clarification and next steps on her breast density classification
Your patient, a 51-year-old postmenopausal woman (G0P0) in good health, had an annual screening mammogram that showed no evidence of malignancy. She is white and has a mother with a history of breast cancer. She has never had a breast biopsy. Following the mammogram, she received a letter from the imaging center, stating:

Your mammogram indicates that you have extremely dense breasts. Dense breast tissue is common and found in more than 40% of women. However, dense breast tissue can make it difficult to detect breast cancer on mammography and dense breast tissue is associated with an increased risk of developing breast cancer. This information is being provided to raise your awareness and to encourage you to discuss with your health care providers your dense breast tissue and other breast cancer risk factors. Together you and your clinicians can decide if additional screening options are right for you.

She calls your office and asks, “What should I do next?”

Breasts are composed of fibrous, glandular, and adipose tissue. If the breasts contain a lot of fibrous and glandular tissue, and little adipose tissue, they are considered to be “dense.” Using mammography, the current standard is to report the density of breast tissue using 4 categories:

  • almost entirely fatty
  • scattered fibroglandular densities
  • heterogeneously dense
  • extremely dense.

Dense breast tissue is defined to include the 2 categories heterogeneously dense and extremely dense.

Observational studies have reported that dense breast tissue is associated with an increased risk of breast cancer, and dense breast tissue makes it more difficult to detect breast cancer on mammography. According to data from the Breast Cancer Surveillance Consortium, among women aged 50 or older, the relative risk of breast cancer stratified by the 4 categories of breast density is 0.59, 1.00, 1.46, and 1.77, for almost entirely fatty, scattered fibroglandular densities, heterogeneously dense, and extremely dense, respectively.1 In one study, the sensitivity of mammography to detect breast cancer was 82% to 88% for women with nondense breasts and 62% to 69% in women with dense breasts.2 These data have catalyzed investigators to explore the use of supplemental imaging to enhance cancer detection in women with dense breasts.

The link between breast density and breast cancer risk and reduced sensitivity of mammography also has catalyzed activists and legislators to champion breast density notification laws, which have passed in more than 20 states. These laws require facilities that perform mammography to notify women with dense breasts that this finding is associated with an increased risk of breast cancer and that dense breasts reduce the ability of mammography to detect cancer. In some states, the law mandates that women with dense breasts be offered supplemental ultrasound imaging and that insurers must cover the cost of the ultrasound studies. Many of the laws recommend that the patient discuss the situation with the clinician who ordered the mammogram.

When I first saw the recommendation for patients to contact me about how to manage dense breasts, my initial response was, “Who? Me?” I felt ill equipped to provide any useful advice and suspected that many of my patients knew more than I about this issue.

Based on a review of the evidence, my current clinical recommendation is outlined in the 2 options below, including a low-resource utilization option and a high-resource utilization option. For patients, physicians, and health systems that are concerned that excessive breast cancer screening tests might cause more harm than benefit, the identification of dense breasts on mammogram is unlikely to be a trigger to perform any additional testing. In this situation, the pragmatic low-resource option is most relevant.

Alternatively, for patients and physicians who strongly believe in the value of screening mammography (see “Utilize tomosynthesis digital mammography technology for your patients” below), a reasonable strategy is to recommend that women with dense breasts and an increased risk for breast cancer be offered supplemental imaging.

In this editorial I elaborate these 2 approaches to breast cancer screening in women with dense breasts.

Utilize tomosynthesis digital mammography technology for your patients

Mammograms are the primary modality used for breast cancer screening because screening mammography has been shown to reduce breast cancer deaths by 15% to 30%.1,2 Annual or biennial mammograms are recommended for women aged 40 years or older by many professional organizations, including the American College of Obstetricians and Gynecologists and the American College of Radiology. However, mammography screening programs have been criticized because of false-positive tests resulting in unnecessary biopsies, limited sensitivity, and the theoretical risk of over-diagnosing clinically insignificant cancers.3,4

Mammography technology continues to evolve. Film-based mammography has been replaced by digital mammography. Tomosynthesis digital mammography, also known as 3-D mammography, is now replacing standard digital mammography.5

With tomosynthesis, digital mammography image acquisition is performed using an x-ray source that moves through an arc across the breast with the capture of a series of images from different angles and reconstruction of the data into thin slices approximately 1 mm in width. The presentation of breast images in thin slices permits superior detection of lesions. In addition, the collected images can be reconstructed to present a virtual 2-D image for analysis.

Tomosynthesis has been demonstrated to increase the sensitivity of mammography to detect cancer and reduce false-positive examinations. In a study of 454,850 mammography examinations, investigators found that the invasive cancer detection rate per 1,000 studies increased from 2.9 with standard digital mammography to 4.1 with tomosynthesis.6

Tomosynthesis also reduces the patient recall rate to perform additional views or subsequent ultrasound. In one large study, the recall rate was 12% for standard digital mammography and 8.4% for tomosynthesis.7

The limitations of tomosynthesis include higher costs and higher radiation doses.

If the technology is available, I recommend that women have their mammograms using the best technology, tomosynthesis digital mammography.8

1. Smith RA, Duffy SW, Gabe R, Tabar L, Yen AM, Chen TH. The randomized trials of breast cancer screening: what have we learned? Radiol Clin North Am. 2004;42(5):793–806.
2. Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening: an independent review. Lancet. 2012;380(9855):1778–1786.
3. US Preventive Services Task Force. Screening for breast cancer: US Preventive Services Task Force recommendations statement. Ann Intern Med. 2009;151(10):716–726, W-236.

4. Welch HG, Passow HJ. Quantifying the benefits and harms of screening mammograms. JAMA Intern Med. 2014;174(3):448–454.
5. Destounis SV, Morgan R, Areino A. Screening for dense breasts: digital tomosynthesis. AJR Am J Roentgenol. 2015;204(2):261–264.

6. Friedewald SM, Rafferty EA, Rose SL, et al. Breast cancer screening using tomosynthesis in combination with digital mammography. JAMA. 2014;311(24):2499–2507.
7. Haas BM, Kalra V, Geisel J, Raghu M, Durand M, Philpotts LE. Comparison of tomosynthesis plus digital mammography and digital mammography alone for breast cancer screening. Radiology. 2013;269(3):694–700
8. Pisano ED, Yaffe MJ. Breast cancer screening: should tomosynthesis replace digital mammography? JAMA. 2014;311(24):2488–2489.


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