Evaluation of serum HER2 extracellular domain in early breast cancer patients: correlation with clinicopathological parameters and survival

Background We explored the correlation between serum human epidermal growth factor receptor-2 (HER2) extracellular domain (ECD) and tissue HER2 status, their relationship with clinicopathological parameters and their impact on disease-free survival (DFS) and overall survival in early breast cancer patients. Patients and methods This prospective trial included patients with stage I–III breast cancer. Serum HER2 ECD levels were measured by two enzyme-linked immunosorbent assays before surgical treatment. Tissue HER2 status was analyzed by immunohistochemistry (IHC) in all tumors; FISH assay was utilized in HER2 2+ tumors by IHC. Results From May 2000 to July 2005, 256 consecutive stage I–III breast cancer patients were included in this study. High serum HER2 ECD levels (≥15 ng/ml) were reported in 23 patients (9.0%) and HER2-positive status in tumor tissue was observed in 42 patients (16.4%) with a concordance of 87.1%. High HER2 ECD levels were significantly associated with high histological grade (P = 0.003), stage III (P = 0.008), lymph node involvment (P = 0.035) and negativity of both estrogen (P = 0.016) and progesterone (P = 0.007) receptors. At multivariate analysis, high serum HER2 ECD levels were a significant independent prognostic factor of worse DFS (P = 0.009). Conclusions A statistically significant association was observed between high serum HER2 ECD levels and worse DFS in early breast cancer patients.