Previous studies have also demonstrated that constitutive expression of COX-2 in human colon cancer cells promotes tumour invasion and the metastatic potential of these cells, and have suggested that COX-2 selective inhibitors can be suitable chemopreventive agents for colorectal cancer (Oshima et al, 1996; Tsuji et al, 1997). This evidence concerns the gene PTGS2 and colonic neoplasm.