Abstract. Detection of circulating tumor cells (CTCs) in peripheral blood is useful for estimating the prognosis of patients with cancer. We previously reported the detection of CTCs by OBP-401, a telomerase-specific, replication-selective, oncolytic adenoviral agent carrying the green fluorescent protein (GFP) gene. We demonstrated that the number of large (L)-GFP+ cells (≥7.735 µm in diameter) in peripheral blood samples correlated significantly with the prognosis of treatment-naïve gastric cancer patients, whereas the number of small (S)-GFP+ cells (<7.735 µm in diameter) did not. In the present study, we studied the change in the number of GFP+ cells during treatment, and analyzed the association between the number of GFP+ cells in blood samples and the outcome of patients. Peripheral blood samples were obtained from 37 gastric patients prior and subsequent to surgery (three samples per time point). Upon infection of blood cells with OBP-401, GFP+ cells of different sizes were counted and measured. The association between the number of GFP+ cells and surgical outcome was determined by statistical analysis. The median follow-up period after surgery was 39 months. Although the difference was not significant, patients with ≥6 L-GFP+ cells in preoperative blood samples had a lower relapse-free survival rate than patients with 0-5 L-GFP+ cells. There was no significant correlation between the number of L-GFP+ cells in postoperative blood samples and the prognosis of patients receiving adjuvant therapy. Although the difference was not significant, the number of S-GFP+ cells in samples from patients who had received postoperative chemotherapy was higher than in those who had not. The number of L-GFP+ cells was not significantly correlated with the relapse-free survival rate in gastric cancer patients who underwent surgery. The number of S-GFP+ cells was relatively high in samples from patients who had received postoperative chemotherapy.
IntroductionThe presence of circulating tumor cells (CTCs) in peripheral blood indicates a systemic disease stage (1), and detection of CTCs in peripheral blood is useful for estimating prognosis and monitoring disease progression in breast (2), prostate (3), skin (4) and colon (5) malignancies. The commonly used techniques for enrichment and detection of CTCs are density gradient separation (6,7), direct enrichment by filtration (8), immunomagnetic separation (9), flow cytometry (10), reverse transcription-polymerase chain reaction (RT-PCR) (11,12) and microchip technology (13). The CELLSEARCH ® System (Veridex LLC, Raritan, NJ, USA) (14) is a widely used automated method of immunomagnetic cell enrichment (15-17) that detects CTCs by detection of epithelial markers such as epithelial cell adhesion molecule (EpCAM) and cytokeratin. The expression of these markers, however, decreases during the epithelial-mesenchymal transition (EMT) (18,19); thus, CTCs undergoing EMT may escape detection.Increased telomerase activity is a common characteristic of malignant tumors, and telomerase ac...