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

Abstract 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.