San Francisco, CA—Magnetic resonance imaging (MRI) screening of women who are at average risk for breast cancer had a mean additional cancer diagnosis yield of 15.8 per 1000 patients, surpassing the yields for digital breast tomosynthesis and ultrasound in a new study. The results were presented at the 2015 Breast Cancer Symposium, by Christiane K. Kuhl, MD, Department of Diagnostic and Interventional Radiology, RWTH Aachen University, Germany. This suggests that breast MRI screening alone every 3 years may be sufficient for women at average risk.
“In this cohort of heavily prescreened women at average risk, the additional cancer yield achieved through MRI was high,” said Dr Kuhl. “Our findings also showed that in average-risk women, the contribution of mammography to early diagnosis will be limited.”
Over- and Underdiagnosis with Mammography
Despite its prevalence of use, mammography leads to problems of over- and underdiagnosis, said Dr Kuhl. Between 30% and 50% of breast cancers are missed by mammography. And because mammography is based on detection of pathophysiologic processes that reflect repressive changes, false positives are also inevitable with this procedure.
MRI, by contrast, will “preferably detect cancers that are biologically active and prognostically relevant,” she said. Nevertheless, MRI screening is currently only being used in high-risk women. There is no evidence for its use in women with an average risk for breast cancer.
This prospective, 2-center, comparative, diagnostic accuracy study included 2120 women who had a total of 3861 MRIs covering 7007 women-years.
The participants (aged 40-70 years) had normal screening mammograms and, in dense breasts, normal screening ultrasound. With no previous breast cancer, no family history of the disease, and no history of tissue diagnosis associated with increased risk, the women were considered “average risk” for breast cancer.
The women were randomized to undergo dynamic contrast-enhanced breast MRI in addition to mammography every 12, 24, or 36 months, plus follow-up of 2 years.
The vast majority (91.0%) of MRIs were read as normal or benign. Women with suspicious findings (4.4%) underwent biopsy. From this group, 35.7% of lesions were ultimately found to be malignant, 24.6% revealed high-risk changes, and 39.8% revealed benign changes.
“This translates into a positive predictive value of 35.7% for cancer,” said Dr Kuhl. “And if you take into consideration that diagnosis of high-risk lesions puts average-risk women into a high-risk category (changing the management of those women), you could argue that the positive predictive value for diagnosis of management-relevant tissue changes is 60.5%.”
Ultimately, 61 cancers were identified in the 2120 women; of these, 60 cancers were only MRI-detected, resulting in an additional cancer yield of 15.8 per 1000 screening rounds.
“The cancer yield was very high in the first-screening round,” said Dr Kuhl. “In other words, the majority  of these cancers were found in the first screening round and dropped significantly during subsequent screening rounds.”
The average additional cancer yield of 15.8 per 1000 women compares favorably with the added cancer yield of 1.25 per 1000 for digital breast tomosynthesis and 4 per 1000 for ultrasound.
“In experienced hands,” said Dr Kuhl, “the false-positive rate of MRI screening in this average-risk cohort was comparable to those of mammographic screening programs or to that of MRI high-risk screening cohorts.”
Dr Kuhl also noted that the added cancers diagnosed by MRI had pathological features of biological importance, skewing toward higher-than-normal high-grade cancers.
“Breast MRI improves the detection of small, high-grade cancers in women at average risk to an extent that the interval cancer rate is zero,” Dr Kuhl concluded.