Role of Diffusion-Weighted Magnetic Resonance Imaging in Prediction of Pathological Complete Response to Neoadjuvant Chemotherapy in Locally Advanced Breast Cancer and Its Molecular Subtypes

Purpose The aim of this study was to evaluate the role of apparent diffusion coefficient (ADC) and hence diffusion-weighted imaging in prediction of pathological complete response (pCR) to neoadjuvant chemotherapy (NACT) in locally advanced breast cancer (LABC) and its molecular subtypes. Methods In this tertiary hospital-based prospective study, 30 patients aged 30 to 65 years, having clinically/cytologically diagnosed LABC, were included. Magnetic resonance imaging (MRI) was done to obtain prechemotherapy ADC (ADC (pre) ), postchemotherapy ADC (ADC (post) ), change in ADC (ΔADC), and ΔADC% for each tumor and its subtype. Postsurgical pCR was used as the reference standard for determining tumor response. All four ADC parameters were compared between pCR and non-pCR groups. Results Of the 30 patients, 19 (63.3%) patients showed pCR, while 11 (36.7%) patients did not. The pCR group showed significantly lower mean ADC (pre) ( p < 0.001) and higher mean ADC (post) ( p < 0.05), ΔADC, and ΔADC% ( p = 0.000) than non-pCR group. The best cutoff values to differentiate responders from nonresponders with receiver operating characteristic curve analysis of ADC (pre) , ADC (post) , and ΔADC% were 0.98 × 10 (−3) mm (2) /s (68.4% sensitivity, 63.6% specificity), 1.31×10 (−3) mm (2) /s (68.4% sensitivity, 63.6% specificity), and 25% (84.2% sensitivity, 90.9% specificity), respectively. Human epidermal growth factor receptor 2 (HER2)-enriched subtype showed significant difference in mean ADC (pre) ( p = 0.045), while triple-negative subtype showed significant differences in mean ADC (post) ( p = 0.032) and mean ΔADC ( p = 0.019) between the two groups. Conclusion ADC (pre) , ADC (post) , and ΔADC can predict pCR to NACT in LABC. Among molecular subtypes, ADC (pre) was predictive only in HER2-enriched subtype, while ADC (post) and ΔADC were predictive only in triple-negative subtype.