Proliferation Determined by Ki-67 Defines Different Pathologic Response to Neoadjuvant Trastuzumab-Based Chemotherapy in HER2-Positive Breast Cancer

BackgroundThis study aimed to assess the role of proliferation measured by Ki-67 as a predictive factor for pathologic complete response (pCR) to trastuzumab-based chemotherapy in patients with human epidermal growth factor receptor 2 (HER2)-positive (HER2+) breast cancer (BC).MethodsA total of 81 patients with HER2+ BC were treated with a sequential schedule consisting of 4 cycles of cyclophosphamide (600 mg/m2) and doxorubicin (60 mg/m2) every 3 weeks, followed by 4 cycles of weekly paclitaxel (80 mg/m2) or docetaxel (100 mg/m2) every 3 weeks combined with trastuzumab (loading dose of 8 mg/kg and then 6 mg/kg every 3 weeks) as neoadjuvant treatment. Histologic subgroups classified by hormone receptor (HR) expression and Ki-67 index were 17% HR+/Ki-67 ≥ 50%, 41% HR+/Ki-67 < 50%, 25% HR–negative (HR−) Ki-67 ≥ 50%, and 17% HR−/Ki-67 < 50%.ResultspCR, defined as the absence of invasive cells in the breast and axillary lymph node, was achieved in 33 patients (41%). The median Ki-67 expression was significantly higher in tumors with pCR (53%) compared with tumors without pCR (30%) (P < .001). Receiver operating characteristic (ROC) curve methodology suggested that 50% was the optimal Ki-67 cutoff point to best identify patients who achieved a pCR. The pCR rate was significantly different between histologic subgroups: HR−/Ki-67 ≥ 50% (70%), HR+/Ki-67 ≥ 50% (71%), HR−/Ki-67 < 50% (22%), and HR+/Ki-67 < 50% (18%) (P < .001). A multivariate analysis revealed that a Ki-67 marker ≥ 50% was the only independent predictive factor of pCR (P = .003; odds ratio [OR], 0.133; 95% confidence interval [CI], 0.036-0.5). The median follow-up was 32 months (range, 14-48 months). Patients who achieved a pCR had significantly lower recurrence (P = .001) and higher overall survival (OS) (P = .013) compared with those who did not. There were no statistically significant differences in disease-free survival (DFS) and OS in relation to HRs, the Ki-67 marker as a continuous or categorical variable, and histologic subgroups.ConclusionProliferation determined by Ki-67 expression ≥ 50% was an independent predictive factor for pCR in patients with HER2+ BC treated with trastuzumab-based chemotherapy.