Since our previous results indicate that the EC CD44+/CD24− population co-localizes with the area of hypoxia [5], we exposed esophageal adenocarcinoma cell line OE33, esophageal adenocarcinoma cell line BE3 and esophageal squamous cell carcinoma cell line OE21 to reduced oxygen levels of 5% O2 for 48 h, compared to the normally used 21%. The gene discussed is CD44; the disease is esophageal squamous cell carcinoma.