SAN FRANCISCO-Magnetic resonance imaging screening improves the detection of biologically relevant breast cancer in women at average risk and reduces the rate of interval cancers down to zero percent, with a low false-positive rate, according to a study reported here at the Breast Cancer Symposium.
But is it practical?
Christiane K. Kuhl, MD, Chair of the Department of Radiology at the University of Aachen, said that among 2,120 asymptomatic women at average risk in the usual age range for screening-mammography (i.e., age 40 to 70), the specificity of MRI-screening was 97.1 percent, with a false-positive rate of 2.9 percent (Abstract 58).
The interval-cancer rate-i.e., finding cancer within 12 months after a negative mammogram-was zero percent, irrespective of the screening interval.
Still, the Discussant for the study said that the report is not likely to end the debate about whether MRI is an appropriate screening tool for breast cancer.
"Breast MRI is currently recommended for screening women at high-risk of breast cancer only, but despite decades of mammographic screening, breast cancer continues to represent a major cause of cancer death for women at average risk as well," Kuhl said. "This suggests a need for improved methods for early diagnosis for these women also."
Prospective Observational Cohort Study
In the prospective observational cohort study she reported at an oral abstract session, participants underwent dynamic contrast-enhanced breast MRI in addition to mammography every 12, 24, or 36 months, along with follow-up for two years to establish a standard of reference.
Breast cancer was diagnosed in 61 of the 2,120 women (DCIS in 20, and invasive cancer in 41). Atypical ductal hyperplasia was detected in 21. Sixty of the cancers were detected only by MRI, one was detected by both MRI and mammography, and none were detected by mammography alone.
The invasive cancers found were small (mean size of 8 mm), were node-negative in 93 percent of patients, and were ER/PR-negative in 33 percent.
"In average-risk women undergoing MRI for screening, the contribution of mammography in early diagnosis will be limited, or absent," Kuhl concluded.
Operative Word: 'Average'
The operative word in this study of average-risk women is "average," said the study's Discussant, Marilyn A. Leitch, MD, Professor and Chair of Breast Surgery at the University of Texas Southwestern Medical Center.
"This was a highly selected population, as 60 of the 61 cancers were MRI-detected, yet the eligibility criteria required that nothing was seen on the mammography prior to the MRI eligibility. Women were excluded if they had an abnormal mammogram, and women with dense breasts also were required to have a normal screening ultrasound."
Leitch listed some of the common concerns about MRI:
* False-positive rates are higher than are reported in this study;
* MRI detects lesions that might drive patients to avoid breast-conserving surgery; and
* There can be unreasonable costs of screening and workup of false-positive results.
"The U.S. Preventive Service Task Force recommends biennial mammography only in women age 50 to 74. And in the [group's] statement in 2009 about MRI as a replacement for mammography, they said the evidence is lacking, and the balance of benefits and harms cannot be determined."
A draft of the Task Force's 2015 document shows it will have similar recommendations, Leitch said.
"So what do we need? A clinical trial."
She said that rather than looking at MRI as a screening tool, what is needed is a trial comparing screening MRI at three-year intervals with digital tomosynthesis in all average-risk women.