Evaluation of Serum HER-2/neu Extracelluar Domain in Breast Cancer Patients: Correlation with Tissue HER-2/neu Status and Clinicopathological Factors

ABSTRACT

PURPOSE: The extracelluar domain (ECD) of HER2 may be cleaved from the surface of cancer cells whereby serum HER2 ECD levels can be detected. We explored the correlation between serum HER2 ECD and tissue HER2 status and their relationship with clinicopathological parameters. METHODS: We included 125 patients with stage 0-3 breast cancer. The serum HER2 ECD level was measured by chemiluminescence immunoassay (ADVIA Centaur(R) system). The tissue HER2 status was analyzed by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) in all tumors. We reviewed the medical records retrospectively. The analyzed clinicopathological parameters were age, tumor size, histologic grade, vascular invasion, lymph node involvement, stage, estrogen receptor (ER) and CA 15-3. RESULTS: High serum HER2 ECD levels (> or =15 ng/ml) were reported in 15 patients (12.0%). For tissue HER 2 status, 30 patients (24.0%) had positive results in FISH and 46 patients (37.0%) had strong positive results in IHC (3+). The specificity of serum HER2 ECD was 92.6% but the sensitivity was only 26.7%. The concordance between serum HER2 ECD and FISH tests was 23.3%. High serum HER2 ECD levels were significantly associated with old age (P=0.005), large tumor size (P=0.021), vascular invasion (P=0.001), lymph node involvement (P=0.010) and advanced stage (P<0.001). ER and CA 15-3 levels were not significantly related with serum HER2 ECD. CONCLUSION: Serum HER2 ECD test could not be substituted for tissue HER2 status because of low concordance. However, high levels of serum HER2 were associated with large tumor size, lymph node involvement and advanced stage. We need to study serum HER2 ECD test as a role of prognostic marker.