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MRI Better Than Mammography at Detecting Early Breast Cancer CME
News Author: Zosia Chustecka
CME Author: Charles Vega, MD


Release Date: August 14, 2007; Valid for credit through August 14, 2008 Credits Available

Physicians - maximum of 0.25 AMA PRA Category 1 Credit(s) for physicians;
Family Physicians - up to 0.25 AAFP Prescribed credit(s) for physicians

August 14, 2007 The earliest stage of breast cancer, ductal carcinoma in situ (DCIS), was detected more accurately by magnetic resonance imaging (MRI) than mammography in a German study published in the August 10 issue of The Lancet.

A direct comparison of the 2 imaging modalities suggested that MRI was nearly twice as effective as mammography. The results come from a group of 167 women who underwent both scans, and who were diagnosed with pure DCIS. They were part of a much larger cohort of 7319 women who were at high risk for breast cancer (eg, because of an abnormal MRI, family history, or clinical symptoms) and who had attended an expert breast cancer center for a period of 5 years.

MRI detected most of the cases of DCIS (153 [92%] of 167), significantly more than the 56% (93 of 153 cases) detected by mammography (P < .0001). In addition, MRI detected nearly all (98%) of the 89 cases that were high-grade DCIS, which is likely to progress to high-grade invasive cancer, the researchers write. In contrast, mammography missed nearly half (48%) of these cases.

This study suggests that the sensitivity of mammography for diagnosing DCIS is limited, conclude the authors, headed by Christiane Kuhl, MD, from the University of Bonn, Germany. They suggest that MRI could help to improve the ability to diagnose DCIS, especially high-grade lesions.

"These findings can only lead to the conclusion that MRI outperforms mammography in tumor detection and diagnosis," comments an accompanying editorial. "The observation that MRI detects many DCIS lesions that go unnoticed on mammography implies that some invasive carcinomas can be prevented by timely intervention on the basis of MRI findings," write Carla Boetes, MD, and Ritse M. Mann, PhD, from the Radboud University Nijmegen Medical Centre in the Netherlands. "As such, MRI has the potential to increase survival when used to detect breast cancer."

Should MRI Be More Than an Adjunct to Mammography?
"MRI should thus no longer be regarded as an adjunct to mammography but as a distinct method to detect breast cancer in its earliest stage," the editorialists conclude. However, not everyone shares this conclusion, and US experts have been quick to step in and say that more data are needed.

This is a single study, and it was performed at an expert center, pointed out Gabriel Hortobagyi, MD, FACP, chair of breast medical oncology at the University of Texas MD Anderson Cancer Center in Houston. "Additional studies will need to be done to support these results," he said in a statement from the American Society of Clinical Oncology (ASCO).

"This is an exciting study," commented Nancy E. Davidson, MD, director of the Breast Cancer Research Program at Johns Hopkins University, and current president of ASCO. She noted that the study was presented at the ASCO annual meeting in June 2007.

However, she added, "This is not a recommendation for routine screening with MRI." When an MRI shows suspicious findings, the next step is a biopsy, and this can be difficult when the lesion is visible only on MRI, she pointed out, adding, "Not many centers are able to perform an MRI-guided biopsy."

The researchers acknowledge that their results come from 1 center with a very high level of expertise, which is unlikely to be found elsewhere. Breast MRI is used only rarely in clinical practice at present, and so few radiologists have had a chance to develop expertise, which they already have with mammography, they comment. "Therefore, our results are unlikely to be reproducible in a community breast imaging service at present," Dr. Kuhl and colleagues write. Nevertheless, they conclude that the current recommendations for use of MRI in screening for DCIS are "not appropriate."

"The implications of the study are clear," says J. Leonard Lichtenfeld, MD, FACP, deputy chief medical officer for the American Cancer Society. "If we are really going to make an impact on reducing the incidence and burden of invasive breast cancer, we must do a better job of finding these high grade DCIS lesions by using MRI routinely in the screening of all women for breast cancer," he writes in a blog on the society's Web page.
However, he adds: "this is not something that is ready for implementation today." The authors themselves do not recommend such a significant policy change, he points out. What they do call for is large clinical trials to compare MRI with mammography, with follow-up to ascertain the impact on outcomes. "Much more needs to be done, including improved certification of centers and radiologists who offer this service," Dr. Lichtenfeld adds. "On those points, all of the experts agree."

MRI Superior to Mammography
The result that MRI seems to be superior to mammography is not a surprise to practitioners who use both imaging modalities. Approached by Medscape for comment, Mitchell D. Schnall, MD, PhD, from the University of Pennsylvania, said that he agrees with the data and much of the editorial comment. "Most of us who do breast MRI know very well that MRI is highly sensitive for all cancer, invasive and DCIS. If you look at the high-risk screening studies (eg, Kriege et al, the MARIBS study, or Werner et al), you will find that MRI will be about 75% sensitive for all cancers and mammography, about 40% sensitive for all cancers."

"Although MRI is twice as sensitive as mammography for all cancers, and more sensitive then mammography for DCIS, it is not perfect," Dr. Schnall continued. "There are still 20% or so cancers that are not detected by MRI, and most of these are DCIS that present with microcalcification. So although MRI alone will outperform mammography alone in detecting invasive cancer and DCIS, as Christiane and Carla both state (and in full disclosure, I consider both of them friends), the addition of mammography to MRI will increase the cancer yield over MRI alone, particularly in the setting of DCIS, by detecting MRI occult lesions that present with calcification. Unless we are prepared to argue that the 10% to 20% additional yield contributed by mammography is not important, it is hard to eliminate mammography from the cancer screening regimen."

"That being said, the value of MRI is clear, and as a single modality it will outperform mammography for invasive cancer and DCIS," Dr. Schnall commented to Medscape.

Another US expert approached for comment was a little more guarded. Judy E. Garber, MD, MPH, from the Dana-Farber Cancer Institute in Boston, Massachusetts, agrees that MRI is superior overall, but pointed out that the results come from a study conducted in a very high-risk population by extremely experienced investigators. "The question will be whether this is the result of superior technology or radiologist skill, or whether there are other reasons that tumors in these high-risk women are not detected with a mammogram," she said.

"Further research should address the sensitivity of MRI in the usual screened population, whether specific populations who would benefit most can be identified, and as for all screening tests the outcome of the lesions identified by MRI to make sure that the impact of MRI is justified beyond its sensitivity," Dr. Garber told Medscape. "The results of the study are provocative and compel further evaluation of MRI screening," she added.

Lancet. 2007;370:459-460, 485-492.

Clinical Context

Nearly all invasive breast cancer is thought to begin as DCIS, although high-grade DCIS is the form that is most likely to progress to become a clinically apparent cancer. The wider use of screening mammography improved the rate of detection of breast cancer at the preinvasive stage from approximately 2% in 1980 to 20% today, but mammography, which focuses on the presence of microcalcifications within DCIS, may be limited in its ability to detect these tumors.

MRI has previously been demonstrated to be inferior to mammography in detecting DCIS. However, the use of diagnostic criteria apart from those used to diagnose invasive breast cancer, particularly a focus on neovascularization, may make MRI more sensitive in finding DCIS. The current study compares the newer diagnostic algorithms of MRI with mammography in the detection of DCIS.

Study Highlights

*Patient data was collected at 1 breast center in Germany. This center generally cares for women with a positive family history of breast cancer and a calculated lifetime risk of breast cancer of 20% or greater.

*The study focused on women who underwent a mammogram and breast MRI between 2002 and 2006.

*These studies were reviewed by radiologists experienced in breast imaging. Findings were classified by criteria from the American College of Radiology Breast Imaging and Data System (BI-RADS). Patients with BI-RADS diagnoses 1, 2, and 3 were considered to have negative studies, whereas BI-RADS categories 4 and 5 were considered positive.

*Patients underwent breast biopsy if the findings on imaging studies or the clinical assessment were suspicious for breast cancer.

*The main outcome of the study was the sensitivity of a positive mammogram and MRI in predicting a positive biopsy result for DCIS.
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*Patients underwent breast biopsy if the findings on imaging studies or the clinical assessment were suspicious for breast cancer.

*The main outcome of the study was the sensitivity of a positive mammogram and MRI in predicting a positive biopsy result for DCIS.

*7319 women underwent mammography and MRI during the study period. 1208 (15%) of these subjects had a positive imaging test, and 167 of the patient cohort received a pathologic diagnosis of DCIS.

*The mean age of subjects was 54.1 years, and 58% of patients were considered to have an average pretest risk of breast cancer. 7% of participants had symptoms suspicious for breast cancer.

*MRI diagnosed 92% of cases of DCIS, compared with only 56% of cases diagnosed with mammography. Rates of false-negative tests were 44% with mammography and 8% with MRI. Both MRI and mammography missed low-grade DCIS in 2 cases.

*In 43% of DCIS cases, only MRI was positive. This compared favorably with mammography, which was positive in only 7% of cases with negative MRI. All 43 cases of high-grade DCIS missed by mammography were diagnosed by MRI.

*Age and risk factors for breast cancer did not affect the rate of positive vs negative mammograms among patients with DCIS, but the presence of necroses increased the sensitivity of mammography in diagnosing high-grade DCIS.

*MRI was particularly more sensitive than mammography in detecting intermediate and high-grade DCIS. The size of the tumor did not affect the sensitivity of the imaging in MRI vs mammography.
Breast density of patients with DCIS diagnosed only by MRI did not differ from those who were diagnosed with DCIS by mammography.

*The overall positive predictive value of mammography was 55%, whereas the positive predictive value of MRI was 59%.

Pearls for Practice

*Most invasive breast cancers develop from DCIS, although a minority of cases are detected at the preinvasive stage. Previous research has suggested that mammography is more sensitive than MRI in detecting DCIS.

*The current study finds that MRI can be more sensitive than mammography in diagnosing DCIS, particularly high-grade DCIS
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