10541 Background: This study was aimed at detecting and HER2-expressiong circulating tumor cells (CTC) in peripheral blood of chemo-naïve or chemo-resistant patients with advanced gastric cancer. 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 age 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 detection and HER2 expression for CTC. Results: We detected ≥1 CTC/7.5ml in 80 of 140 patients (57.1%). HER2-positive CTC were observed in 19 of 80 CTC-positive patients (23.8%), including 6 patients with HSR2-negative primary tumors. 21 patients with HER2-positive primary tumors administered trastuzumab in combination with chemotherapy (Xeloda+cisplatin; 15, weekly Paclitaxel; 5). We detected ≥1 CTC/7.5ml 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. Conclusions: HER2 expression on CTC was associated with chemo-resistance. Information on the HER2 status of CTC might be helpful for stratification of HER2-directed therapies.
Serum HER2 levels and HER2 status in tumor cells in advanced gastric cancer patients