Purpose: Diffusion-weighted imaging (DWI) with the calculation of an apparent diffusion coefficient (ADC) has been proposed as a quantitative biomarker on contrast-enhanced (CE) MRI of the breast. There is a need to approve a generalizable ADC cut-off. The purpose of this study was to evaluate whether a pre-defined ADC cut-off allows downgrading of BI-RADS 4 lesions on CE-MRI, avoiding unnecessary biopsies. Experimental Design: This was a retrospective, multicentric, cross-sectional study. Data from five centers were pooled on the individual lesion level. Eligible patients had a BI-RADS 4 rating on CE-MRI. For each center, two breast radiologists evaluated the images. Data on lesion morphology (mass, non-mass), size, and ADC were collected. Histology was the standard of reference. A previously suggested ADC cut-off ({greater than or equal to}1.5*10-3 mm2/s) was applied. A negative likelihood ratio of 0.1 or lower was considered as a rul e-out criterion for breast cancer. Diagnostic performance indices were calculated by Receiver Operating Characteristics (ROC) analysis. Results: There were 657 female patients (mean age 42, standard deviation 14.1) with 696 BI-RADS 4 lesions included. Disease prevalence was 59.5% (414/696). The area under the ROC curve was 0.784. Applying the investigated ADC cut-off, sensitivity was 96.6% (400/414). The potential reduction of unnecessary biopsies was 32.6% (92/282). Conclusions: An ADC cut-off of {greater than or equal to}1.5*10-3 mm2/s allows downgrading of lesions classified as BI-RADS 4 on breast CE-MRI. One-third of unnecessary biopsies could thus be avoided.
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