O2-034 - Detection and HER2 Expression of Circulating Tumor Cells in Advanced Gastric Cancer Patients

Abstract

ABSTRACT Purpose This study was aimed at detecting and HER2-expressiong circulating tumor cells (CTC) in peripheral blood of chemo-naive or chemo-resistant patients with advanced gastric cancer. Materials and methods All patients were enrolled using institutional review board-approved protocols at the Cancer Institute Hospital in the Japanese Foundation for Cancer Research and provided informed consent. The study population consisted of patients of aged 18 years or older with histologically proven advanced gastric cancer. A total of 140 patients with advanced gastric cancer were enrolled into a prospective study. We used CellSearch system for the detection and HER2 expression for CTC. Results We detected more than or equal to 1 CTC/7.5 ml in 80 of 140 patients (57.1%). HER2-positive CTC were observed in 19 of 80 CTC-positive patients (23.8%), including six patients with HSR2-negative primary tumors. Twenty-one patients with HER2-positive primary tumors administered trastuzumab in combination with chemotherapy (Xeloda + cisplatin; 15, weekly paclitaxel; 5). We detected more than or equal to 1 CTC/7.5 ml at the baseline in 11 of 20 patients with trastuzumab treatment. HER2-positive CTCs were observed in 6 of 11 CTC-positive patients (54.5%). Patients with HER2-positive CTC at the baseline were shorter PFS than those with HER2-negative CTC at the baseline. Conclusion HER2 expression on CTC was associated with chemoresistance. Information on the HER2 status of CTC might be helpful for stratification of HER2-directed therapies.