The Octamer 4 gene (Oct4) is a master pluripotency con-troller that has been detected in several types of tumors. Here, we examine the expression of Oct4 in human esophageal squamous cell carcinoma (ESCC). We found that punctate Oct4 protein was expressed in most (93.7%) ESCC samples but it was not observed in esophageal mu-cosa. Some ESCC cells had the capacity to form tumoro-spheres; those with an Oct4⁺-rich cell phenotype had in-creased proliferation and Oct4 mRNA levels compared to those of differentiated cells in culture or xenograft tumors. The over-expression of Oct4 in ESCCs suggests that it is a potential target for ESCC therapy. Oct4 could be a useful tumor marker in an immunohistochemical panel designed to differentiate between ESCC and esophageal mucosa. Expression of Oct4 in tumorospheres might indicate the presence of a population of ECSCs and its expression in xenograft tumors suggests that Oct4 is also associated with tumor metastasis.

Keywords: esophageal cancer stem cell, esophageal squamous cell carcinoma, Nanog, Oct4, Sox2