Dense Breasts: Who Needs More Imaging?

Kenneth W. Lin, MD


January 08, 2020

Editorial Collaboration

Medscape &

This transcript has been edited for clarity.

Hi, everyone. I'm Dr Kenny Lin. I am a family physician at Georgetown University Medical Center, and I blog at Common Sense Family Doctor.

I vividly remember the first time I diagnosed a patient with an interval breast cancer. She'd had a normal screening mammogram just 6 months before, but came in complaining of a new breast lump. My heart sank as I began my examination, as I had little doubt from its appearance that this lump represented an invasive cancer that either had not been present at the time of her mammogram or had not been detected by the test.

It's harder to find breast cancer on a mammogram in women with dense breast tissue, and these women are also at slightly higher risk for breast cancer. About two thirds of states have passed laws requiring that a woman be notified when her mammogram shows dense breasts, and a recent study suggested that women are more likely to be aware of breast density and its relationship to cancer risk than in the past. However, primary care physicians in states that have passed such laws often feel poorly prepared to counsel women regarding what action to take, if any, for a woman with dense breasts and a normal mammogram.

In a previous Medscape commentary, I voiced concerns about a draft US Food and Drug Administration (FDA) regulation that would require specific language about breast density in lay patient mammography reports, despite the lack of evidence that supplemental screening with ultrasound or MRI improves outcomes. Others have since expressed similar sentiments, noting that the FDA's proposed wording is too complex for a woman with average or low health literacy to understand; that supplemental imaging is known to increase false-positive findings, unnecessary biopsies, and costs, and possibly overdiagnosis; and that the opportunity cost of discussing supplemental screening could crowd out other preventive care discussions that are more likely to lead to health benefits.

In California, women with higher breast density were more likely to undergo supplemental MRI after passage of a breast density notification law in 2013. To test the hypothesis that MRI could reduce the rate of interval breast cancers, a multicenter trial in the Netherlands randomly assigned women aged 50-75 years with extremely dense breast tissue to mammography only or mammography plus an invitation to MRI. About 60% of women in the MRI-invitation group actually had the MRI. After 2 years, the interval cancer rate in the MRI group was half that of the mammography-only group, an absolute difference of one interval cancer prevented for every 400 screenings.

The study results have been largely portrayed in the media as proof of the effectiveness of MRI in women with dense breasts, though in fact it was not designed to compare such health outcomes as morbidity or mortality from breast cancer. We don't know how many additional tumors detected by MRI at the expense of more false-positive results and biopsies were overdiagnosed or would have eventually presented clinically, or whether earlier treatment of the clinically important tumors was more likely to result in cure. If the draft FDA regulation goes into effect, by the time such patient-oriented evidence is available, millions more US women will probably have undergone MRI without knowing if it is truly helpful or harmful.

Reflecting on the rapid adoption of 3-D mammography in clinical practice, Drs Joy Melnikow and Joshua Fenton recently wrote:

Diffusion of medical technology ahead of definitive evidence is common in the United States. ...When the evidence from randomized clinical trials catches up, interventions shown to add little value to previous approaches to care are often already embedded in practice, widely covered by health insurance (sometimes by mandate), and difficult to withdraw.

A natural desire to help women and impatience on the part of physicians and patients for definitive evidence regarding the most beneficial approach to breast density is driving the current push for additional screening for women whose breast cancers may be missed by mammography. I certainly have wondered if my first patient, and others I've since diagnosed with interval cancers, may have lived longer or had fewer treatment harms if MRI had advanced their time to diagnosis. But mandating discussions about breast density in the absence of evidence-based guidance could easily do more harm than good.

This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.

Kenneth W. Lin, MD, MPH, teaches family medicine, preventive medicine, and health policy at Georgetown University School of Medicine. He is deputy editor of the journal American Family Physician.

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