ObjectiveTo investigate whether the addition of diffusion-weighted imaging (DWI) to dynamic contrast-enhanced MRI (DCE-MRI) improves diagnostic performance in predicting pathologic response and residual breast cancer size following neoadjuvant chemotherapy. Materials and methodsA total of 78 consecutive patients who underwent preoperative breast MRI with DWI following neoadjuvant chemotherapy were enrolled. DWI was performed on a 1.5T system with b values of 0 and 750s/mm. or on a 3T system with b values of 0 and 800 or 0 and 1000s/mm. The images on DCE-MRI alone, DWI alone, and DCE-MRI plus DWI were retrospectively reviewed. We evaluated the diagnostic performances of the three MRI protocols for the detection of residual cancer. The tumor size as predicted by MRI was compared with histopathologic findings. Apparent diffusion coefficient (ADC) values were also compared between the groups with and without residual cancer. ResultsOf the 78 patients, 59 (75.6%) had residual cancer. For detection of residual cancer, DCE-MRI plus DWI had higher specificity (80.0%), accuracy (91.0%), and PPV (93.2%) than DCE-MRI or DWI alone (P=0.004, P=0.007, and P=0.034, respectively). The ICC values for residual cancer size between MRI and histopathology were 0.891 for DCE-MRI plus DWI, 0.792 for DCE-MRI, and 0.773 for DWI. ADC values showed no significant differences between residual cancer and chemotherapeutic changes (P=0.130). ConclusionsThe addition of DWI to DCE-MRI significantly improved diagnostic performance in predicting pathologic response and residual breast cancer size after neoadjuvant chemotherapy.