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Diffusion-weighted imaging shows promise identifying false-positive lesions
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Diffusion-weighted imaging successfully identified as negative/benign nearly half of nonmalignant breast lesions that had been incorrectly identified as positive by MRI, according to results of a retrospective study.
Savannah C. Partridge, PhD, research associate professor in the department of radiology at the University of Washington Seattle Cancer Care Alliance, and colleagues reviewed diffusion-weighted imaging characteristics of nonmalignant lesion subtypes that had been classified as category 4 or 5 false positives using MRI.
The study included 175 breast lesions that were suspected of malignancy and recommended for biopsy using conventional breast MRI, but were found to be benign on the biopsy.
The lesions under analysis were taken from 165 women. Apparent diffusion coefficients from diffusion-weighted imaging (b = 0, 600 sec/mm2) were calculated for each sample, according to the results. Researchers then conducted a comparison between subtypes with an apparent diffusion coefficient threshold of 1.81 × 10−3 mm2/sec.
Forty-six percent of lesions yielded coefficients greater than the prespecified threshold. Certain lesion subtypes were more likely to have coefficients above the threshold, including:
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fibroadenoma ([1.94 ± 0.38 {standard deviation}] × 10−3 mm2/sec; n = 30)
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focal fibrosis ([1.84 ± 0.48] × 10−3 mm2/sec; n = 19)
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normal tissue ([1.81 ± 0.47] × 10−3 mm2/sec; n = 13)
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apocrine metaplasia ([2.01 ± 0.38] × 10−3 mm2/sec; n = 13)
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usual ductal hyperplasia ([1.83 ± 0.49] × 10−3 mm2/sec; n = 12)
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inflammation ([1.95 ± 0.46] × 10−3 mm2/sec; n = 10).
“We have previously found that breast cancers typically exhibit lower apparent diffusion coefficient values than benign lesions on diffusion-weighted imaging,” Partridge told HemOnc Today. “We defined a useful diagnostic apparent diffusion coefficient threshold or cut-off to best differentiate benign and malignant lesions without missing any cancers.”
The most common lesion subtype to have a coefficient below the threshold was atypical ductal hyperplasia ([1.48 ± 0.36] × 10−3 mm2/sec; n = 23).
The lowest mean coefficient among nonmalignant lesions was reported for lymph nodes ([1.28 ± 0.23] × 10−3 mm2/sec; n = 4).
The most common lesions with apparent diffusion coefficients below the threshold were atypical ductal hyperplasia and lobular neoplasia. These lesions had significantly lower coefficients than for other benign lesions (P,.0001).
“Assessing [apparent diffusion coefficients] along with dynamic contrast-enhanced MR imaging features may decrease the number of avoidable false-positive findings at breast MR imaging and reduce the number of preventable biopsies,” the researchers concluded.
If the apparent diffusion coefficient threshold had been added to the conventional MRI assessment so that only suspicious lesions with apparent diffusion coefficient values below the cut-off were biopsied, 46% of the benign lesions could have avoided biopsy, Partridge said.
“They exhibited high apparent diffusion coefficient values, above the diagnostic threshold value,” Partridge said. “Essentially it is additional criteria radiologists can use to decide whether or not a lesion they see on MRI is suspicious for malignancy to help reduce unnecessary biopsies.”
Disclosure: The study was supported by a grant from NIH.
Perspective
Back to TopAlexander B. Sevrukov, MD
The latest in research evaluating the role of diffusion-weighted imaging in breast MRI, this study provides additional evidence that diffusion-weighted imaging may be a promising adjunct to dynamic contrast-enhanced imaging with a potential to improve specificity of breast MR by decreasing the false-positive biopsy rate of MR-detected lesions. The authors correctly indicate that the clinical utility of diffusion-weighted imaging and the use of a specific ADC threshold requires further validation in prospective trials.
A significant overlap in ADC values of malignant and nonmalignant lesions presents the greatest challenge in using a set threshold to inform the decision to avoid a biopsy. Challenges in widespread clinical use of this method may also include limited access to advanced breast MR imaging and interpretation expertise for women in the community setting. As image acquisition and post-processing technology improves and becomes more available, diffusion-weighted imaging may find a more permanent place in the breast MR toolkit.
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