Survival Outcomes of Zo-NAnTAx: a Five-Year Analysis of Zoledronic Acid Added to a Neoadjuvant Regimen for HER2-positive Breast Cancer.

Background:Zoledronic acid (ZA) improved outcomes in breast cancer. In pre-clinical studies, ZA increased tumour regression in combination chemotherapy and anti-human epidermal growth factor receptor 2 (HER2) target therapy. The Zo-NAnTax study, a clinical trial combining ZA with neoadjuvant therapy for HER2-positive tumours met the primary endpoint, showing a higher pathological complete response (pCR) rate than predicted in patients receiving surgery. Here, we report the exploratory relapse-free survival (RFS) and overall survival (OS) analysis after five years of follow-up. Methods:Adult women with HER2-positive breast cancer amendable to curative surgery who consented to the study received four cycles of ZA at 4 mg + doxorubicin 60 mg/m2 + cyclophosphamide 600 mg/m2 followed by four cycles of ZA at 4 mg + docetaxel 100 mg/m2 + trastuzumab 6 mg/kg (8 mg/kg as a loading dose), all in a 21 days-cycle, totalizing 8 cycles before surgery. To achieve the primary endpoint of pCR rate between 22% and 35%, 56 patients were needed. The secondary endpoints included safety, gene expression according to treatment response, prediction of pCR rate by an interim breast magnetic resonance imaging (bMRI). Results:Beyond the overall pCR rate of 42%, alongside a good safety profile, we showed similar pCR rates in both hormonal receptor (HR) positive (40%) and HR-negative (44%). RFS and OS at five years were evaluated in 58 subjects, and the overall rate was 79.3% and 86.2%, respectively. Numerically higher values of both RFS and OS were observed in patients achieving pCR vs. non-achieving, respectively 83.3% vs. non-pCR 76.5% (P=0.57) and 95.8% vs. non-pCR 79.4% (P=0.08). Although not statistically significant, OS was numerically equivalent according to HR status, respectively 85.7% vs. 87.5% for HR-positive and HR-negative (P=0.91), which contrasted with RFS, HR-positive 81% vs. HR-negative 75% (P=0.58). None of the assessed clinicopathological biomarkers significantly correlated with survival. Conclusions:ZA plus neoadjuvant therapy in HER2-positive breast cancer shows provoking survival outcomes. Clinical and pre-clinical investigation with dual anti-HER2 blockage is warranted.