Quercetin, which is a natural flavonoid, also showed COX-2 inhibitory effects, similar to those of commercially available COX-2 inhibitors (NS-398 and nimesulide), on cell proliferation, apoptosis, PGE2 production, and COX-2 mRNA expression in the OE33 human oesophageal adenocarcinoma cell line [36]. Here, PTGS2 is linked to esophageal adenocarcinoma.