PTGS2 and esophageal squamous cell carcinoma: We and others have shown that (i) COX-2 expression is a frequent phenomenon in human ESCC tissue samples and positive expression is related with lymphatic metastasis [16, 18–22], (ii) COX-2 inhibitors can inhibit tumor cell proliferation and induce apoptosis by inducing G0 / G1 cell cycle arrest and suppressing Bcl-2 expression [15, 23] as well as prevent tumor formation in vivo through the inhibition of COX-2 [14].