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Undiagnosed breast cancer at MR imaging: analysis of causes.

PURPOSE
To retrospectively review the causes of false-negative results on prior magnetic resonance (MR) imaging studies in patients who developed breast cancer as revealed on a follow-up MR imaging study and to determine the presumptive causes of these false-negative findings.


MATERIALS AND METHODS
Fifty-eight pairs of MR imaging studies from one institution were assessed, consisting of a prior study without a diagnosis of cancer and a diagnostic study with subsequent findings of 60 cancers in 58 women at MR imaging (mean interval between prior and diagnostic MR examinations, 13.8 months). Two radiologists reviewed in consensus, in a nonblinded fashion, each pair of MR studies, comparing the diagnostic and the prior MR imaging studies to evaluate the rate of false-negative findings. The prospective reports were then analyzed to classify false-negatives findings in breast enhancement of breast cancers not identified at the time of imaging, potentially misinterpreted, and mismanaged. False-negative results on prior MR studies were retrospectively reassessed to identify possibly reasons why cancers had been not recognized, potentially misinterpreted, or mismanaged.


RESULTS
Twenty-eight (47% [95% confidence interval {CI}: 34%, 59%]) of the 60 cancers were retrospectively diagnosed as Breast Imaging Reporting and Data System grade 3, 4, or 5 lesions. Analysis of the prospective reports showed that six lesions (10% [95% CI: 2%, 18%]) had been not identified at the time of diagnosis, 15 lesions (25% [95% CI: 14%, 36%]) were potentially misinterpreted, and seven lesions (12% [95% CI: 3%, 20%]) were mismanaged. The main causes of misinterpretation were smooth margins of a mass (n=4), stability in size (n=3), and location of a nonmass in a postsurgical area (n=5). Mismanagement was mainly due to inadequate correlations between MR imaging and ultrasonographic (US) features, with inaccurate sampling with US guidance in five cases.


CONCLUSION
In patients with breast cancer seen at MR imaging, retrospective evaluation of the prior MR imaging studies showed potential observer error in 47% of cases, resulting more from misinterpretation than from nonrecognition or mismanagement of cancers.