Circulating tumor cells are predictive of poor response to chemotherapy in metastatic gastric cancer

Background: The aim of this study was to investigate the impact of number of circulating tumor cells (CTCs) on the treatment outcome for metastatic gastric cancer (GC) following palliative chemotherapy. Methods: CTCs were isolated from 7.5 mL of whole blood from 100 patients with metastatic GC by anti-EpCAM antibody coated magnetic particles using the CTC-Profiler (Veridex). Correlations between CTC counts and clinicopathological variables, progression-free survival and overall survival were examined. Results: Between January 2010 and August 2010, 100 metastatic GC patients were enlisted. Among 100 patients, 5 or more CTCs (CTC-positive) were detected in 27 of 95 patients (28%). Even though the clinical characteristics of the CTC-positive and CTC-negative groups were not significantly different, the treatment response to cytotoxic chemotherapy in the CTC-positive group was significantly poorer (progressive disease: 23.4% vs. 60.0% in CTCnegative vs. CTC-positive group, respectively; p = 0.004). The median progression-free survival of the CTC-positive group was substantially shorter than that of the CTC-negative group (59 days vs. 141 days; p = 0.004). For overall survival, CTC-positive group had significantly shorter survival than CTC-negative group (median OS, 120 days vs. 220 days; p = 0.030). A multivariate Cox proportional hazards regression model showed that CTC positivity was an independent adverse factor for progression-free survival and overall survival. Conclusions: This study suggests CTCs are associated with poor response to chemotherapy in metastatic GC patients.