Evaluation of serum HER2 extracellular domain in in metastatic gastric or gastroesophageal junction cancer: Correlation with HER2 status by immunohistochemistry and fluorescence in situ hybridization and clinicopathologic parameters.

Abstract

4107 Background: To explore the association between serum human epidermal growth factor receptor-2 (HER2) extracellular domain (ECD) and tissue HER2 status, their relationship with clinicopathological parameters and impact on overall survival (OS) in metastatic gastric or gastro-oesophageal junction (GEJ) adenocarcinoma. Methods: A total of 219 histologically confirmed inoperable locally advanced, recurrent, or metastatic gastric or GEJ adenocarcinoma were included. Serum HER2 ECD was measured by chemiluminescent assay. Tissue HER2 status was accessed by fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC) assay. Results: The median serum ECD level was 9.3 ng/ml (range 3.0 to >350). Tissue HER2 status was positive (IHC3+ or 2+ with FISH amplification) in 37 patients (16.9%) and negative in 182 patients (83.1%). Statistically significant associations were found between serum HER2 ECD level and HER2 status assessed by IHC and FISH. The ROC-analysis suggested the cutoff of 16.35 ng/ml (24 of 219 patients had HER2 ECD >16.35 ng/ml ) could produce a sensitivity of 51.4% and a specificity of 97.3% to predict tissue HER2 status. If the cutoff value was increaseed to 22 ng/ml, then all 12 patients with serum HER2 ECD >22 ng/ml were HER 2 positive in primary tumor, corresponding to a specificity of 100% and a sensitivity of 32.4%. High serum HER2 ECD levels were strongly associated with liver metastasis (P < 0.001), the intestinal histologic type (Lauren's classification) (P =0.003), large number of metastais (>2) (P=0.012) and increased LDH level (P < 0.001) . High serum HER2 ECD levels were more common in GEJ adenocarcinoma although the difference had no stastical significance. HER2 ECD levels did not show a significant impact on OS. Conclusions: A significant association was observed between serum HER2 ECD levels and tissue HER2 status in metastasis gastric or GEJ adenocarcinoma. The high specificity of serum HER2 ECD assay to predict tissue HER2 status suggests its potential use as a surrogate marker of the HER2 status in gastric cancer.