Esophageal cancer stem cells and implications for future therapeutics

Esophageal carcinoma (EC) is a lethal disease with high morbidity and mortality worldwide, and the incidence has been increasing in recent years. Although the diagnosis and treatment of EC have improved considerably, EC has rapidly progressed in the clinical setting and has a poor prognosis for its metastasis and recurrence. The general idea of cancer stem cells (CSCs) is primarily based on clinical and experimental observations, indicating the existence of a subpopulation of cells that can self-renew and differentiate. The EC stem cells, which can be isolated from normal pluripotent stem cells by applying similar biomarkers, may participate in promoting esophageal tumorigenesis through renewal and repair. In this review, major emphasis is given to CSC markers, altered CSC-specific pathways, and molecular targeting agents currently available to target CSCs of esophageal cancer. The roles of numerous markers (CD44, aldehyde dehydrogenase, CD133, and ATP-binding cassette subfamily G member 2) and developmental signaling pathways (Wnt/β-catenin, Notch, hedgehog, and Hippo) in isolating esophageal CSCs are discussed in detail. Targeting CSCs can be a logical strategy to treat EC, as these cells are responsible for carcinoma recurrence and chemoradiation resistance.