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. Here, CA9 is linked to squamous cell carcinoma.