Significance of the ADC ratio in the differential diagnosis of breast lesions

Background Magnetic resonance imaging (MRI) has high sensitivity but low specificity for breast cancer, and consequently, new techniques to improve the specificity of breast MRI in diagnosing breast cancer are under development. Purpose To assess the ability of the apparent diffusion coefficient (ADC) compared with the ADC ratio (ADCr) to differentially diagnose benign compared with malignant breast lesions. Material and Methods Forty-eight women with breast lesions (average age, 45 years) underwent MRI scanning including T1-weighted dynamic contrast-enhanced (DCE) scanning and diffusion-weighted imaging (DWI). The average ADC and ADCr values for both lesions and pectoralis major muscles (ADC(rmuscle) and ADCr(muscle)) were measured in patients with malignant (n=25) and benign (n=23) breast lesions. The ADCr of the contralateral breast (ADCr (contralateral)) was also evaluated. All histology was confirmed by pathological analysis of biopsied tissue. ADC and ADCr values were analyzed using receiver-operating characteristic (ROC) curves. Results For benign lesions compared with malignant lesions, lesion-side ADC was 1.45 vs. 1.05, respectively (P<0.001), normal-side ADC was 1.82 vs.1.64 (P=0.002), ADC(rmuscle) was 1.35 vs. 0.9 (P<0.001), and ADCr(contralateral) was 0.79 vs. 0.64 (P=0.001). ADCr(muscle) showed higher sensitivity (82.61%) and specificity (96.00%) than ADCr(contralateral) (60.87% and 92.00%, respectively) and ADC (69.57% and 96.00%) for discriminating malignant from benign lesions. The AUC using ADCr(muscle) had higher discriminatory power (0.92, P<0.001) for malignant versus benign breast lesions compared with either ADC (0.82, P<0.001) or ADCr(contralateral) (0.78, P=0.001). Conclusion The ADCr(muscle) value showed higher sensitivity and specificity and improved diagnostic accuracy compared with either ADC or ADCr(contralateral) in differentiating benign from malignant breast lesions.