610 Background: In breast cancer patients, accurate diagnosis of ductal spreading is of great importanace for deciding sugical procedure. The role of imaging diagnosis using 3D-MRI in deciding of ductal spreading was assessed histologically and efficacy of 3D-MRI guided surgery was evaluated. Methods: Preoperative 3D-MRI was underwent 374 cases of breast cancer patients. Images were obtained 371 cases (99%). These patients could be divided into four groups according to 3D-MRI images: pattern 1) localized type, 2) widely enhanced type A (enhanced area: less than Quadrant) and 3) widely enhanced type B (enhanced area: more than Quadrant) and 4) multifocal type. Diagnosis of ductal spreading was confirmed histologically and relation between 3D-MRI patterns and ductal spreading were assessed retrospectively. Local failure of 3D-MRI guided surgery was assessed by 3D-MRI image patterns Results: The rate of histological confirmed ductal spreading were seen in 59% (125/212cases), 86% (49/57 cases) and 83% (19/23cases) of patients with 3D-MRI pattern 1), 2), and 3), respectively. From April 2005, resected specimen was serially step cut and total specimens were evaluated. Tumor diameter from nipple side to lateral margin were measured by MRI and resected specimens, tumor size was correlated between MRI and resected specimens, significantly (n=80, r=0.790887, P < 0.001). Whole breast examination revealed that only 4 cases were multifocal cancer in 17 cases of multifocal image in 3D-MRI. Patient selection for breast conserving surgery was based by 3D-MRI images. The proportion of breast-conserved surgery were obtained 96% (203/212 cases), 86% (49/57 cases), 26% (6/23cases) and 89% (68/76 cases) of patients with 3D-MRI pattern 1), 2), 3), and 4), respectively. Local failures were seen 2cases in pattern 1), one case in 3) and one case in 4) (2–77 months, median follow up 39 months). Conclusions: These results suggest that MRI will be the useful breast imaging tool in diagnosing ductal spreading and tumor size in breast cancer patients. Safety breast conserving surgery was achieved by MRI guided surgery. No significant financial relationships to disclose.