Apparent Diffusion Coefficient Values for Discriminating Benign and Malignant Breast MRI Lesions: Effects of Lesion Type and Size

The purpose of this study was to determine whether lesion type and size affect discrimination of benign and malignant breast lesions with diffusion-weighted MRI. This study included 91 women with 116 breast lesions identified with dynamic contrast-enhanced MRI. Diffusion-weighted images were acquired during clinical breast MRI at b values of 0 and 600 s/mm(2). Differences in the apparent diffusion coefficients (ADCs) of benign and malignant lesions were compared by lesion type (mass or nonmasslike enhancement) and size ( 1 cm), and receiver operating characteristics analysis was performed to evaluate diagnostic performance based on ADC thresholds. Sixteen of 71 masses and 13 of 45 lesions with nonmasslike enhancement were malignant. The mean ADC was significantly lower for malignant than for benign lesions for both masses (mean difference, 0.49 x 10(-3) mm(2)/s; p < 0.001) and lesions with nonmasslike enhancement (mean difference, 0.20 x 10(-3) mm(2)/s; p = 0.02). The area under the receiver operating characteristics curve (AUC) was greater for masses (AUC, 0.80) than for lesions with nonmasslike enhancement (AUC, 0.66). The mean ADC for malignant masses (1.25 x 10(-3) mm(2)/s) was lower than that for malignant lesions with nonmasslike enhancement (1.41 x 10(-3) mm(2)/s; p = 0.07). The median lesion size was 1.1 cm (range, 0.5-8.3 cm); 45 of 71 masses (63%) measured 1 cm or smaller, and 37 of 45 lesions with nonmasslike enhancement (82%) were larger than 1 cm. There was no relation (p > 0.05) between ADC value and lesion size for benign or malignant lesions, and there were no differences in AUC based on lesion size (p > 0.05). Diffusion-weighted MRI shows promise in differentiation of benign and malignant masses and lesions with nonmasslike enhancement found at breast MRI and is not affected by lesion size. However, ADC measurements may be more useful for discriminating masses than for discriminating lesions with nonmasslike enhancement.