Role of the Apparent Diffusion Coefficient in the Prediction of Response to Neoadjuvant Chemotherapy in Patients with Locally Advanced Breast Cancer

Background We evaluated the diagnostic performance of the baseline diffusion weighted imaging (DWI) and the apparent diffusion coefficient (ADC) in the prediction of a complete pathologic response (pCR) to neoadjuvant chemotherapy (NAC) in patients with breast cancer stratified according to the tumor phenotype. Patients and Methods We retrospectively studied 225 patients with stage II, III, and IV breast cancer who had undergone contrast-enhanced magnetic resonance imaging (MRI) and DWI before and after NAC, followed by breast surgery. Results The tumor phenotypes were luminal (n = 143; 63.6%), triple-negative (TN) (n = 37; 16.4%), human epidermal growth factor receptor 2 (HER2)-enriched (n = 17; 7.6%), and hybrid (hormone receptor-positive/HER2+; n = 28; 12.4%). After NAC, a pCR was observed in 39 patients (17.3%). No statistically significant difference was observed in the mean ADC value between a pCR and no pCR in the general population (1.132 ± 0.191 × 10-3 mm2/s vs. 1.092 ± 0.189 × 10-3 mm2/s, respectively; P =.23). The optimal ADC cutoff value in the general population was 0.975 × 10-3 mm2/s (receiver operating characteristic [ROC] area under the curve [AUC], 0.587 for the prediction of a pCR). After splitting the population into subgroups according to tumor phenotype, we observed a significant or nearly significant difference in the mean ADC value among the responders versus the nonresponders in the TN (P =.06) and HER2+ subgroups (P =.05). No meaningful difference was seen in the luminal and hybrid subgroups (P =.59 and P =.53, respectively). In contrast, in the TN and HER2+ subgroups (cutoff value, 0.995 × 10-3 mm2/s and 0.971 × 10-3 mm2/s, respectively), we observed adequate ROC AUCs (0.766 and 0.813, respectively). Conclusion The pretreatment ADC value is not capable of predicting the pCR in the overall population of patients with locally advanced breast cancer. Nonetheless, an ameliorated diagnostic performance was observed in specific phenotype subgroups (ie, TN and HER2+ tumors).