DUOX2 protein was undetectable in normal stratified squamous epithelium of esophagus (Figure 2(a1)); however, in the columnar epithelium of Barrett esophagus, the DUOX2 protein was detected in the apical membrane of epithelial cell although some epithelial cells have positive stains in the cytoplasm (Figure 2(a2)). This evidence concerns the gene DUOX2 and Barrett esophagus.