Background: Epithelial cell adhesion molecule (EpCAM) is a marker for circulating tumor cells (CTCs) in various type of cancer including esophageal squamous cell carcinoma (ESCC). Cell surface antigens, such as CD90 and CD44, have been reported to be cancer stem cell (CSC) markers in ESCC. The aim of this study was to assess the use of CD90 and CD44 as markers to identify clinically significant CTC subpopulations in ESCC. Methods: Three ml of peripheral blood was collected from 10 ESCC patients and 10 healthy volunteers to detect combined expression of EpCAM, CD90 and CD40 using flow cytometry. Results: The number of EpCAM-positive cell counts (average ± SD) in the patients was significantly higher than healthy volunteers (29.1 ± 35.9 and 2.3 ± 2.5, p=0.001). The proportion (average ±SD) of CD90- and CD44- positive cells in EpCAM-positive cells were 45.7 ± 42.4% and 98.7 ± 2.7%, respectively. EpCAM-positive/CD44-positive CTC counts, which was equivalent to EpCAM-positive CTC counts, correlated with pathological v factors in the resected primary tumors (p>0.01). EpCAM-positive/CD90-positive CTC counts, but not EpCAM-positive/CD90-negative CTC counts, correlated with pathological v factors in the resected primary tumors (p=0.01). Our result suggested that combined expression of EpCAM and CD90 may useful to detect CTC subset which have highly metastatic features in ESCC. While CD44 is equivalent to EpCAM as a marker to detect CTCs in ESCC.

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