MCM4 and Barrett esophagus: Previously constructed tissue microarrays consisting of samples of 7 tissue types (columnar cell metaplasia, Barrett esophagus, low- and high-grade dysplasia, esophageal adenocarcinoma, squamous epithelium, and squamous cell carcinoma) were used for the immunostaining of CA9, BMI1, cyclin E, Ki67, MCM4 and MCM7.