OBJECTIVETo evaluate the accuracy of MRI for estimating residual tumor size after neoadjuvant chemotherapy (NAC) with three-dimensional (3D) reconstruction technique.

METHODSThis was a prospective study. The data of 61 patients with pathologically proven solitary invasive ductal carcinoma (IIA-IIIC) who had received 6 to 8 cycles of NAC from July 2010 to August 2013 was analyzed. All the patients were female, aging from 31 to 70 years with a median of 49 years. Breast specimen after surgery was prepared with part-mount sub-serial section, and residual tumors were microscopically outlined, scanned and registered by Photoshop software. The 3D model of pathological and MRI residual tumors was reconstructed with 3D-DOCTOR software. The longest diameter, maximum cross-section area and volume of the residual tumors determined using 3D MRI were compared with 3D pathological findings, and the associations between MRI and pathology were analyzed by Spearman rank correlation and Bland-Altman analysis.

RESULTSThe longest diameter, maximum cross-section area and volume of the residual tumors after NAC measured by MRI and pathology was highly correlated (r=0.942, 0.941, 0.903, all P=0.00). MRI appears to underestimate pathology in the longest diameter, maximum cross-section area, but slightly overestimate in volume, and two methods had a good consistence (MD=0.3 cm, 95% CI: -1.43 to 1.9 cm; MD=1.39 cm², 95% CI: -9.55 to 12.34 cm²; MD=-0.433 cm³, 95% CI: -7.065 to 6.199 cm³).

CONCLUSION3D MRI reconstruction after NAC could accurately detects the residual tumors after neoadjuvant chemotherapy, and contribute to select patients who received breast conserving therapy after NAC with tumor downstaging.