Background Use of neoadjuvant chemotherapy necessitates assessment of response to cytotoxic drugs.The aim of this research was to investigate the effectiveness of dynamic contrast-enhanced magnetic resonance imaging (MRI) for evaluating clinical responses to neoadjuvant chemotherapy in breast cancer patients.Methods We examined patients receiving neoadjuvant chemotherapy for primary breast cancer between October 2007and September 2008.Dynamic contrast-enhanced MRI was used to examine breast tumors prior to and after neoadjuvant chemotherapy.The MRI examination assessed tumors using Response Evaluation Criteria in Solid Tumors (RECIST).The Miller-Payne grading system was used as a histopathological examination to assess the effect of the treatment.We examined the relationship between the results of RECIST and histopathological criteria.In addition,we used time-signal intensity curves (MRI T-SI) to further evaluate the effects of neoadjuvant chemotherapy on tumor response.Results MRI examination of patients completing four three-week anthracycline-taxanes chemotherapy treatment revealed that no patients had complete responses (CR),58 patients had partial responses (PR),29 patients had stable disease (SD),and four with progressive disease (PD).The effectiveness of neoadjuvant chemotherapy (CR + PR) was 63.7% (58/91).The postoperative histopathological evaluations revealed the following:seven G5 (pCR) cases (7.7%),39G4 cases (42.9%),16 G3 cases (17.6%),23 G2 cases (25.3%),and six G1 cases (6.6%).The effectiveness (G5 + G4 +G3) was 68.1% (62/91).MRI T-SI standards classified 53 responding cases,29 stable cases,and nine progressing cases.These results indicated that the treatment was 58.2% effective (53/91) overall.Conclusions Dynamic contrast-enhanced MRI and histopathological standards were highly correlated.Importantly,MRI T-SI evaluation was found to be useful in assessing the clinical effectiveness of neoadjuvant chemotherapy.