Objective:To investigate the value of dynamic contrast-enhanced MRI enhancement amplitude for qualitative diagnosis of suspicious residual enhancing lesions after neoadjuvant therapy (NAT) in breast cancer.Methods:In total, 168 suspicious residual enhancing lesions of 168 patients who received NAT at Peking University Cancer Hospital from January 2015 to June 2016 were retrospectively analyzed and divided into non-residual cancer group ( n=59) and residual cancer group ( n=109) according to pathological findings. Then 168 suspicious residual enhancing lesions were stratified according to molecular subtype and baseline enhancing morphology. According to the breast imaging reporting and data system, the morphology of enhancing lesions, the margin of mass-like enhancing lesions, and the distribution of non-mass-like enhancing lesions on MRI before NAT were recorded. The second phase (1 min 45 s-2 min after contrast injection) was used as the early phase, and the fifth phase (5-6 min after contrast injection) was used as the late phase to measure the signal intensity and time-signal intensity curve (TIC) of suspicious residual enhancing lesions, and the signal enhancement ratio (SER) was calculated. Independent sample t-test, Mann-Whitney U test and χ 2 test were used to compare the difference of SER and clinical features between the non-residual and residual cancer groups. The receiver operator characteristic curve was used to analyze the diagnostic efficacy of SER to determine residual cancer. Results:There are statistically significant differences in invasive ductal carcinoma grade, hormone receptor status, the morphology of enhancing lesion on baseline MRI and TIC type between non-residual and residual cancer groups ( P<0.05). The SER values of the non-residual cancer group in the early [31% (23%, 61%)] and late (72%±43%) enhanced phases were significantly lower than those of the residual cancer group [49% (28%, 71%), 88%±38%, Z=-2.26, t=-2.43, P=0.024, 0.016, respectively]. Among suspicious residual enhancing lesions with hormone receptor negative status and single mass-like morphology, the SER values of the non-residual cancer group in the early (33%±16%) and late [64% (42%, 74%)] enhanced phases were significantly lower than those of the residual cancer group [59%±30%, 84% (77%, 106%), t=-2.86, Z=-3.17, P=0.008, 0.001, respectively]. The area under the curve values of SER in differentiating suspicious residual enhancing lesions were statistically different between early and late enhanced phases (0.606 and 0.637, respectively, Z=2.16, P=0.031). Conclusion:For breast cancer after NAT, it is difficult to determine the suspicious residual enhancing lesions on MRI subjectively, especially the hormone receptor negative lesions with single mass, SER can be used as an auxiliary diagnostic method, and it is necessary for the analysis of late enhancement.