MILAN, ItalyIn women with fibroglandular or dense breasts,
magnetic resonance imaging (MRI) is more sensitive than mammography for
detection of multiple malignant foci, suggesting that a dynamic MRI examination
is warranted before treatment planning in this group of patients, a team of
Italian radiologists and surgeons has concluded. Yet in breasts with an almost
completely fatty pattern, both techniques had comparable sensitivity, their
multicenter, prospective, nonrandomized study showed. Further, while MRI
achieved a 17% gain in sensitivity over mammography in detection of invasive
foci, the two techniques had similar sensitivity in detection of in situ foci,
and neither had a strong positive predictive value (PPV), the researchers
In their analysis of 99 breasts in 90 women with planned
mastectomies who underwent both diagnostic techniques, with pathologic
examination of the whole excised breast used as the gold standard, mammography
missed more larger and invasive cancer foci than MRI.
The team, led by Francesco Sardanelli, MD, of the Department
of Diagnostic Imaging, Istituto Policlinico San Donato, Milan, Italy, noted
that their results were expected and confirmed findings of several large series
indicating that MRI has significantly greater sensitivity than mammography for
correct diagnosis of multifocal, multicentric cancer (Am J Radiol
The value of pathologic analysis of the whole excised breast
in this study, they said, is that it provided a true picture of the proportion
of false-negative findings with mammography and MRI, adding that, to their
knowledge, theirs is the first large study to use a whole-breast pathologic
exam as a gold standard for evaluating mammography vs MRI in detection of
multifocal, multicentric disease.
The global trend toward a conservative surgical approach to
breast cancer, they emphasized, should be based on exclusion of undetected
malignant foci in the breast, which they noted are frequently responsible for
relapses after conservative surgery.
The 18-center trial was performed between 1998 and 2000. All
participating sites had proven breast imaging experience. Of 153 patients
enrolled, 90 were evaluable. The women in the study had a mean age of 59 years
(range, 43 to 75). They had proven breast cancer and planned mastectomies, 9 of
which were bilateral, for a total of 99 breasts examined. Prior to surgery, the
patients underwent both mammography and gadolinium-enhanced dynamic MRI. After
imaging, pathologic exams of the entire excised breast were performed onsite.
All examinations were evaluated for the presence of
malignant foci by a team of two off-site radiologists who were aware that
mastectomies were planned but were blinded to the results of the pathologic
examination. A third radiologist compared the location of the breast foci in
pathologic sections, on mammography, and on MRI, using a nine-region map of
eight segments plus the nipple region.
A database created through this lesion-matching process
enabled investigators to perform analyses on both a lesion-by-lesion and a
breast-by breast basis. Based on the pathologic report, cancer was diagnosed as
unifocal when a single malignant focus was found, as multifocal when more than
one malignant focus was shown in the same segment or in adjacent segments of
the map, and as multicentric when foci were identified in noncontiguous
Pathology revealed a total of 188 malignant foci (158
invasive, 30 in situ) among the 99 breasts examined: 52 lesions were unifocal,
29 were multifocal, and 18 were multicentric.
The overall sensitivity for detection was 66% for
mammography and 81% for MRI (P < .001). MRI also had 17% greater
sensitivity in detecting invasive foci (72% for mammography vs 89% for MRI,
P < .001). However, the two techniques were not significantly different in
their detection of in situ foci (mammography 37%, MRI 40%, P > .05).
Mammography missed a total of 64 malignant foci and MRI
missed a total of 36; the median diameter of missed foci was 8 mm with
mammography vs 5 mm with MRI (P = .033). Both mammography and MRI
detected the nine cases of bilateral cancer.
Striking differences between the techniques were noted in
dense or fibroglan-dular breasts (see Figures 1 and Figures 2), for which
mammography and MRI had sensitivities of 60% and 81%, respectively (P <
.001); the PPV of the techniques was similar, however, at 78% and 71%,
In contrast, results in breasts with an almost completely
fatty pattern showed that sensitivity of mammography vs MRI was comparable, at
75% and 80%, respectively, as was their PPV, at 73% and 65%, respectively, with
neither difference reaching statistical significance. The overall PPV was not
significantly different for either diagnostic technique, at 76% for mammography
and 68% for MRI
(P > .05).
In terms of staging of the lesions, both techniques
correctly staged only 51% of the breasts, with mammography under-staging 30%
and overstaging 19% of the remaining breasts; conversely, MRI understaged 19%
and overstaged 30% of remaining breasts.
In discussing the results, the investigators commented that,
while a PPV of 76% for mammography might be considered noteworthy, the
technique was associated with a total of 40 false-positive lesions in the
study, and the high PPV seen "can be attributed in large part to selection of
potential candidates for mastectomy with almost two (1.9) malignant foci per
breast, of whom 47% had multifocal, multicentric cancer."
They speculated that the fact that 19% of malignant foci
were undetected by MRI may have been a result of their small size (5 mm, vs 8
mm for foci detected by MRI), or perhaps a low level of angiogenesis.
The investigators concluded that MRI may be most practical
following a second "conventional evaluation" such as a "second mammography to
acquire tailored views or magnifications, or a targeted sonography after MRI,"
adding that MRI-guided breast biopsy should be performed when MRI-detected foci
are undefined. Because their findings confirmed that, like mammography, the
specificity of MRI is "relatively low," they concluded that "availability of
MRI-guided biopsy [should be] mandatory for centers that intend to use MRI as a
The investigators suggested that the specificity of MRI
could be improved "by integrating the best morphologic and dynamic data, by
means of proton MR spectroscopy, and by the use of short-term antiestrogen (tamoxifen)
medication before MRI."
Further gains in sensitivity of MRI, they wrote, might be
achieved by increasing the in-plane and through-plane spatial resolution.
Going forward, the research team emphasized that only
further research can determine the true clinical value of using only MRI to
detect malignant foci in the breast, noting that "randomized studies comparing
the outcome of patients undergoing pretreatment MRI are needed to define the
effects of a more precise evaluation of the extent of disease on relapse rate,
quality of life, and survival rate."