CD44 and esophageal squamous cell carcinoma: Subsequently, we analyzed the correlation between the reported ESCC CSC markers (SOX2, OCT4, Nanog, ABCG2, CD90, BMI1, P75NTR, CD271, CD44, CD133) and the mRNA level of these 12 proteins in ESCC in TCGA database, and found that MSI2 had the highest correlation with the ESCC CSC markers (Figure 7A).