Objective:To investigate the value of whole-lesion histogram parameters of apparent diffusion coefficient (ADC) in evaluating and predicting the pathological complete response(PCR) to neoadjuvant chemotherapy (NAC) in different subtypes of breast cancer.Methods:This retrospective study included 117 patients with breast cancer who underwent MRI examination before NAC prior to surgery from January 2016 to December 2017 in the First Affiliated Hospital of Nanjing University. All cases were divided into Luminal B, HER2 positive ( n=21) and triple negative ( n=26) groups. The surgical pathology after chemotherapy was evaluated by Miller-Payne (M-P) system and the patients were divided into PCR group and non-PCR (nPCR) group. Firevoxel software was used to generate the whole-lesion ADC histogram. The parameters included mean (ADC mean), skewness, kurtosis, the minimum (ADC min), the maximum (ADC max), 10th percentile(ADC 10%), 50th percentile (ADC 50%) and 90th percentile (ADC 90%). The two independent samples t test or Mann-Whitney U test was used to compare the differences between PCR and nPCR groups in each subtype. The diagnostic performance of statistically different ADC parameters for predicting PCR was evaluated by receiver operating characteristic (ROC) curve. Results:Kurtosis was significantly higher in PCR group than that in nPCR group in HER2 positive subtype ( P=0.039). It achieved an area under the curve (AUC) of 0.813 with sensitivity of 100% and specificity of 68.7% at the optimal cutoff value (1.861) for differentiating PCR from nPCR cases. In triple negative subtype, ADC mean and ADC 50% were smaller in PCR group than those in nPCR group ( P=0.028,0.013). They achieved AUCs of 0.800, 0.842, respectively. When ADC mean of 1.030×10 -3 mm 2/s and ADC 50% of 0.976×10 -3 mm 2/s were used as cutoff value to differentiate PCR from nPCR, the sensitivities were 75.0%, 80.0% and the specificities were 83.3%, 83.3%, respectively. Conclusion:Kurtosis can predict post-NAC PCR in patients with HER2 positive breast cancer, while ADC 50% has a high value in predicting post NAC PCR of triple negative breast cancer patients.