GGCT and esophageal squamous cell carcinoma: γ-Glutamylcyclotransferase (GGCT, 188 amino acids, 21 kDa) is an enzyme involved in glutathione metabolism [1], and has recently been described to be overexpressed in a variety of cancers (breast, ovarian, cervical, lung, urinary bladder, colon cancers, osteosarcoma, esophageal squamous cell carcinoma, and glioma) and as a critical player in cancer cell proliferation [2].