Patient-Oriented Evidence That Matters
Supplemental MRI Screening in Women with Very Dense Breasts Reduces Interval Cancer Rate but May Cause Overdiagnosis
Am Fam Physician. 2020 Jun 1;101(11):695-696.
Does supplemental magnetic resonance imaging (MRI) screening for women with very dense breasts reduce the number of interval cancers?
Supplemental MRI screening for women with very dense breasts compared with mammography alone every two years significantly reduces the likelihood of an interval cancer, from 5 per 1,000 to 2.5 per 1,000 in the intention-to-treat population and to 0.8 per 1,000 in the per-protocol population. False-positive results were common, and there were more overall and early-stage cancers detected in the MRI group, raising the concern that many of these cancers may have been present but growing slowly and indolently (so-called overdiagnosed cancers). Subsequent follow-up will hopefully determine whether mortality and not just incidence is affected. (Level of Evidence = 1b−)
Most guidelines recommend mammography every two years, typically in women 50 to 69 or 75 years of age. The only exception is the American College of Radiology, which continues to recommend annual screening. In this Dutch study, women undergoing routine digital mammography who were identified as having very dense breast tissue (grade 4/4) and who had a normal digital mammogram result were randomized in a 1:4 ratio to receive supplemental MRI screening or usual care. After randomization, the women in the MRI group were notified and invited to participate. Obtaining consent after randomization is known as a Zelen design and is thought to reduce protocol violations and anxiety in the women not randomized to MRI. Women with a Breast Imaging Reporting and Data System (BI-RADS) MRI score of 4 or 5 were recalled for further evaluation, including biopsy. Women with a BI-RADS score of 3 had a second reading of the MRI, and if the second reading was also 3, they had a follow-up MRI in six months. The primary outcome was the likelihood of interval cancer, defined as all cancers detected in the 24 months following a negative index digital or MRI mammogram
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