Prognostic Factors in HER2-Positive Primary Breast Cancer Patients Treated Using Neoadjuvant Chemotherapy Plus Trastuzumab

Background: It is unclear for whom new anti-human epidermal growth factor receptor 2 (anti-HER2) agents, such as pertuzumab and T-DM1, should be considered. We investigated prognostic factors before neoadjuvant chemotherapy (NAC) among HER2-positive invasive breast cancer patients and those after NAC among patients who did not achieve pathological complete response (pCR) using conventional adjuvant trastuzumab. Methods: HER2-positive primary breast cancer patients treated using NAC containing trastuzumab were enrolled between September 2006 and June 2017 at the Osaka Breast Clinic. Patients with distant metastasis or using NAC containing pertuzumab were excluded. The main outcome was disease-free survival (DFS). We investigated pre- and post-NAC prognostic factors using the log-rank test and Cox proportional hazards model. Results: In total, 157 patients were included. Among the pre-NAC prognostic factors, younger age (under 40 years old) and positive clinical nodal status were significantly poorer prognostic factors (hazard ratio [HR] 3.47, 95% CI 1.06–10.12, p = 0.041 and HR 3.32, 95% CI 1.03–14.78, p = 0.045) by multivariate analysis. Among the post-NAC prognostic factors, patients with non-pCR (3-year DFS; 85 vs. 96%, p = 0.022) had a poorer DFS than patients with pCR. DFS was assessed for non-pCR patients (n = 64). High post-NAC Ki-67 status (≥20%; HR 6.73, 95% CI 1.82–31.93, p = 0.004) was a significant and large post-NAC tumor size (≥2 cm; HR 3.65, 95% CI 0.97–14.71, p = 0.056) was a marginally significant prognostic factor by multivariate analysis. After having combined them, high post-NAC Ki-67 status or large post-NAC tumor size was also a significant prognostic factor (HR 5.75, 95% CI 1.32–16.12, p = 0.017). Conclusions: Positive clinical nodal status and young age were found to be prognostic factors before NAC in HER2-postive invasive breast cancer patients. A high post-NAC Ki-67 status and large post-NAC tumor size were significant and marginally significant prognostic factors, respectively, after NAC in patients who did not achieve pCR. New anti-HER2 agents, such as pertuzumab and T-DM1, should be considered for the patients with those prognostic factors.