MRI Ups Early Breast Cancer Diagnosis in Women With Dense Breasts

Veronica Hackethal

November 27, 2019

Having dense breasts is a double-edged sword when it comes to screening for breast cancer: dense breast tissue may increase the risk for breast cancer as well as complicate the detection of tumors with screening mammogram.

Whereas American guidelines do not yet recommend supplemental screening, doctors may choose to follow up negative mammograms with MRI in women with dense breasts. Until now, very little data has supported this practice.

Now, a randomized controlled trial has provided the first high-quality evidence that using MRI in addition to screening mammography may improve early detection of breast cancer in women with extremely dense breasts. 

Results were published online today in the New England Journal of Medicine.

"We found that supplemental screening with MRI in women with extremely dense breast tissue resulted in the diagnosis of significantly fewer interval cancers than the use of mammography alone," write lead author Marije F. Bakker, PhD, University Medical Center Utrecht, the Netherlands, and colleagues with the DENSE Trial Study Group.

The study showed that using MRI roughly cut in half the number of interval cancers compared with screening mammogram alone.

Interval cancers are those found during the time period between screening tests — in this case, breast tumors found during the regular 2-year interval after a negative screening mammogram and before the next regularly scheduled screening mammogram. A reduction in interval cancers may indicate that these cancers have been detected earlier, before they could become symptomatic and cause disease or death. 

Results from the study also suggested that using supplemental MRI detected more slow-growing, less aggressive cancers. Many of these tumors were also early stage, well differentiated tumors that were hormone receptor-positive, and potentially more treatable than later-stage tumors.

Yet not all tumors that are detected early actually progress to cause symptoms or death. So the question remains whether detecting breast cancer earlier using MRI translates into improved survival for women with dense breasts.

"It is unclear how many of the cancers detected in our trial were life-threatening and what fraction, if any, represents overdiagnosis," the authors write.

Moreover, supplemental MRI had a false positive rate of 8%. And almost 74% of women who had MRI and went on to breast biopsy did not actually have breast cancer.

"[If we use supplemental MRI], will we be putting these women at increased risk of procedures without contributing to their eventual survival?" asked Dan Longo, MD, in an accompanying editorial. Longo, who was not involved with the study, is a professor of medicine at Harvard Medical School in Boston, Massachusetts, and deputy editor of the New England Journal of Medicine.

"The findings of this trial are likely to reinforce the idea that MRI screening is important in women with dense breast tissue," he continued, but the study cannot answer the question of whether the tumors that were detected  "needed to be found or treated."

Larger, longer-term studies are needed to answer these questions, according to both the authors and editorialist.

"The ultimate test of the value of MRI screening in women with extremely dense breast tissue will be whether its use improves survival — an answer that we will not have for a very long time," Longo concludes.

Study Details

The study took place as part of a population-based screening program at eight hospitals and four regional screening centers in the Netherlands between December 2011 and November 2015. It included 40,373 women aged 50 to 75 years who had extremely dense breast tissue and normal results on screening mammogram. Of these, 8061 women were chosen at random to be invited to supplemental MRI, while 32,312 were assigned to mammogram screening alone. Data on cancer diagnoses came from the Netherlands Cancer Registry.

Fifty-nine percent of women offered MRI accepted the invitation (n = 4783).

Women in the MRI group had a lower overall rate of interval cancers (2.5 per 1000 screenings) compared with the mammogram-only group (5.0 per 1000 screenings), for a statistically significant rate difference of 2.5 per 1000 screenings (95% confidence interval, 1.0 to 3.7; P < .001).

Among women who received MRI, 454 (9.5%) women had abnormal scans and were called back for further testing. A total of 300 of these women (6.3%) went on to breast biopsy. Of these, 79 actually had breast cancer: 64 (81%) of these were invasive tumors, and 15 (19%) were ductal carcinoma in situ (a form of early cancer with low risk of becoming invasive). Most of these cancers were early stage 0 or I (n = 72), node negative (n = 70), moderately to well differentiated (n = 55), and hormone receptor-positive (n = 56).

Supplemental MRI had a sensitivity of 95.2% and a specificity of 92%. Among women who had MRI and were called back for additional testing, 17.4% actually had breast cancer. Among women who had MRI and breast biopsy, 26.3% actually had breast cancer.

Among women who underwent MRI, 0.1% had an adverse event such as vasovagal responses, contrast reactions, or intravenous line infiltration.

The study was funded by the University Medical Center Utrecht, the Netherlands Organization for Health Research and Development, the Dutch Cancer Society, the Dutch Pink Ribbon–A Sister’s Hope, Bayer Pharmaceuticals, and Stichting Kankerpreventie Midden-West. Volpara Health Technologies provided Volpara Imaging Software for screening units.

Bakker reports grants from ZonMw (government), Dutch Cancer Society, the Dutch Pink Ribbon–A Sister's Hope, Bayer AG Pharmaceuticals, and Stichting Kankerpreventie Midden-West during the conduct of the study. Several coauthors have similar disclosures. Editorialist Longo is deputy editor of the New England Journal of Medicine and has disclosed no other relevant financial relationships. 

N Engl J Med. Published online November 27, 2019. Abstract, Editorial

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