From the Journals

Supplemental MRI found to benefit women with dense breast tissue



The use of supplemental MRI screening in women with extremely dense breast tissue and normal results on mammography led to the diagnosis of significantly fewer interval cancers, compared with mammography alone during a 2-year screening period, results from a randomized trial show.

Breast cancer cells Dr. Cecil Fox/National Cancer Institute

“Women with extremely dense breast tissue have an increased risk of breast cancer, and their cancers are also less likely to be detected on mammography,” Dutch researchers led by Marije F. Bakker, PhD, of Utrecht (The Netherlands) University and colleagues wrote for the Dense Tissue and Early Breast Neoplasm Screening (DENSE) Trial Study Group in an article published in the New England Journal of Medicine.

“Such patients may benefit from a tailored breast-screening strategy, supplemented with more sensitive imaging methods. The benefit of supplemental imaging is the subject of a worldwide debate. In the United States, a federal law directs breast-density reporting, but supplemental screening is not recommended in American guidelines. Although supplemental imaging increases the rate of cancer detection in women with dense breasts, the question remains whether it improves health outcomes,” they said.

In the DENSE trial, researchers assigned 40,373 women with extremely dense breast tissue and negative results on screening mammography to a group that was invited to undergo supplemental MRI or to a group that received mammography screening only. The women were between the ages of 50 and 75 years and were enrolled between December 2011 and November 2015 as part of the Dutch population-based digital mammography screening program. The primary outcome was the between-group difference in the incidence of interval cancers during a 2-year screening period.

Dr. Bakker and associates found that the interval cancer rate was 2.5 per 1,000 screenings among 4,783 women in the MRI invitation group, compared with 5 per 1,000 among the 32,312 women in the mammography-only group, a difference of 2.5 per 1,000 screenings (P less than 0.001). Among the women who were invited to undergo MRI, 59% actually underwent the procedure. Of the 20 interval cancers diagnosed in the MRI-invitation group, 4 were diagnosed in the women who had undergone MRI, which translated to 0.8 per 1,000 screenings. The remaining 16 were diagnosed in those who had not undergone MRI, which translated into 4.9 per 1,000 screenings.

“Undergoing supplemental MRI was associated with a cancer-detection rate of 16.5 per 1,000 screenings and resulted in a false positive rate of 8.0% (79.8 per 1,000 screenings),” the researchers wrote. “Of the women who underwent a breast biopsy on the basis of an MRI indication, 26.3% had breast cancer and 73.7% did not.”

Dr. Bakker and coauthors acknowledged certain limitations of the trial, including the fact that it was not large enough to examine the effect of MRI screening on breast cancer–specific or overall mortality. “This outcome would require a much larger sample size and longer follow-up,” they wrote. “The lower rate of interval cancers that we found among participants who underwent MRI is indicative of and prerequisite for an effect on mortality. After that, a reduction in the number of advanced cancers would also be required to show a mortality benefit, which would require several years of follow-up.”

In an accompanying editorial, Dan L. Longo, MD, noted that the study provides high-quality data from a randomized trial where none existed (N Engl J Med. 2019 Nov 27. doi: 10.1056/NEJMe1912943). “It appears to show that among women with dense breasts, the risk of interval cancers is halved by following a negative mammogram with MRI screening,” wrote Dr. Longo, who is deputy editor of the New England Journal of Medicine, as well as professor of medicine at Harvard Medical School, Boston. “But is a reduction in interval cancers an appropriate surrogate for improved overall survival? It appears that most of the cancers that were detected on supplemental MRI screening were found at an early stage. Ductal carcinoma in situ was 10 times more frequent among patients undergoing MRI, and these diagnoses were likely to lead to treatments. What remains unclear is whether the tumors would never otherwise have been detected or threatened the patient’s survival.”

The trial was supported by the University Medical Center Utrecht (the Netherlands), the Netherlands Organization for Health Research and Development, the Dutch Cancer Society, the Dutch Pink Ribbon–A Sister’s Hope organization, Stichting Kankerpreventie Midden-West, and Bayer Pharmaceuticals, with an in-kind contribution from Volpara Health Technologies.

The researchers reported having no relevant financial disclosures other than the trial funding. Dr. Longo is employed by the New England Journal of Medicine as deputy editor.

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SOURCE: Bakker MF et al. N Engl J Med. 2019 Nov 27. doi: 10.1056/NEJMoa1903986.

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