Accuracy of ultrasound shear-wave elastography in predicting pathologic response after neoadjuvant chemotherapy for breast cancer

Objective To assess the value of using shear-wave elastography (SWE) to predict response of patients with breast cancer following neoadjuvant chemotherapy (NAC). Methods Between Oct. 2012 to Jun. 2013, 43 patients with 44 invasive breast cancer tumors diagnosed by ultrasound guided core needle biopsy (CNB) were retrospectively reviewed. All the 43 patients underwent 4-8 periods of standard NAC and the rates of max stiffness values estimated by SWE was compared with histological findings. Pathologic response in breast cancer was classified into five grades according to Miller & Payne histopathological grading system. The response of NAC was defined as effective (CR+ PR), the reduction rate of max SWE value ≥30%; stable disease (SD), the reduction rate of max SWE value <30%; progressive disease (PD), SWE value increase. CR+ PR correlated with the major pathologic response (G3+ G4+ G5); SD+ PD correlated with the minor pathologic response (G1+ G2). The sensitivity, specificity and agreement rate of SWE value was determined by comparing with the final surgical hispathological results which was the gold standard. The agreement of NAC response between SWE and surgical hispathological results was measured using Kappa statistics. The difference of max SWE value between before and after NAC of both groups of major and minor pathologic response was measured using paired t tests. The difference of max SWE value before and after NAC was measured respectively between group of major and minor pathologic response using independence t tests. Results According to Miller& Payne histopathological grading system, pathological response of all the 44 breast tumors underwent NAC was: 3 G1, 6 G2, 24 G3, 8 G4 and 3 G5 (35 major pathologic responses and 9 minor pathologic response). The reduction rate of max SWE value <30% (SD+ PD) was 11 in 44 cases and the reduction rate of max SWE value ≥30% (CR+ PR) was 33 in 44 cases. The SWE values of all the tumors decreased. The sensitivity, specificity and accordance rate of SWE to predict response to NAC was 88.6%, 77.8% and 86.3%. The agreement between SWE results and surgical excision findings was satisfied and Kappa value was 0.61. The max SWE value before and after NAC have no differences between groups of major and minor pathologic response [(180.6±51.7) kPa vs (144.2±66.1) kPa, t=1.431, P=0.338; (76.5±45.3) kPa vs (109.6±47.4) kPa, t=1.372, P=0.189] . There was also no difference between max SWE value before and after NAC of group of minor pathologic response [(144.2±66.1) kPa vs (109.6±47.4) kPa, t=3.353, P=0.028] . However, there was significant difference between max SWE value before and after NAC of group of major pathologic response [(180.6±51.7) kPa vs (76.5±45.3) kPa, t=7.906, P=0.000] . Conclusion SWE was a convenient, accurate methods in predicting responds to NAC in patients with breast cancer. Key words: Breast neoplasms; Elasticity imaging techniques; Chemotherapy, adjuvant; Treatment outcome