AIM: To evaluate the epithelial-to-mesenchymal transition(EMT) of circulating tumor cells(CTCs) in gastric cancer patients.METHODS: We detected tumor cells for expression of four epithelial(E~+) transcripts(keratins 8, 18, and 19 and epithelial cell adhesion molecule) and two mesenchymal(M~+) transcripts(Vimentin and Twist) by a quantifiable, dual-colorimetric RNA-in situ hybridization assay. Between July 2014 and October 2014, 44 patients with gastric cancer were recruited for CTC evaluation. Blood samples were obtained from selected patients during the treatment course [before surgery, after surgery and at the 6~(th) cycle of XELOX based chemotherapy(about 6 mo postoperatively)].RESULTS: We found the EMT phenomenon in which there were a few biphenotypic E~+/M~+ cells in primary human gastric cancer specimens. Of the 44 patients, the presence of CTCs was reported in 35(79.5%) patients at baseline. Five types of cells including from exclusively E~+ CTCs to intermediate CTCs and exclusively M~+ CTCs were identified(4 patients with M~+ CTCs and 10 patients with M~+ or M~+ > E~+ CTCs). Further, a chemotherapy patient having progressive disease showed a proportional increase of mesenchymal CTCs in the post-treatment blood specimens. We used NCI-N87 cells to analyze the linearity and sensitivity of Can Patrol~(TM) system and the correlation coefficient(R~2) was 0.999.CONCLUSION: The findings suggest that the EMT phenomenon was both in a few cells of primary tumors and abundantly in CTCs from the blood of gastric cancer patients, which might be used to monitor therapy response. AIM: To evaluate the epithelial-to-mesenchymal transition (EMT) of circulating tumor cells (CTCs) in gastric cancer patients. METHODS: We detected tumor cells for expression of four epithelial (E ~ +) transcripts (keratins 8, 18, and 19 and epithelial cell adhesion molecule) and two mesenchymal (M ~ +) transcripts (Vimentin and Twist) by a quantifiable, dual-colorimetric RNA-in situ hybridization assay. Between July 2014 and October 2014, 44 patients with gastric cancer were recruited for CTC evaluation. Blood samples were obtained from selected patients during the treatment course [before surgery, after surgery and at the 6th (th) cycle of XELOX based chemotherapy (about 6 mo postoperatively)]. RESULTS: We found the EMT phenomenon in which Of the 44 patients, the presence of CTCs was reported in 35 (79.5%) patients at baseline. Five types of cells including from exclusively E ~ + CTCs to intermediate CTCs and exclusi Further, a chemotherapy patient has progressive disease showed a proportional increase of mesenchymal CTCs in the post-treatment blood specimens. We used NCI-N87 cells to analyze the linearity and sensitivity of Can Patrol ™ system and the correlation coefficient (R ~ 2) was 0.999.CONCLUSION: The findings suggest that the EMT phenomenon was both in a few cells of primary tumors and abundantly in CTCs from the blood of gastric cancer patients, which might be used to monitor therapy response.