**10.4 Ursodeoxycholic acid**

The protective role of ursodeoxycholic acid for CRC is probably due to the reduced absorption of the secondary deoxycholic acid, which increases epithelial proliferation and promote carcinogenesis. A study proved that use of synthetic ursodeoxycholic acid is associated with reduced risk of development of CRC in patients with ulcerative colitis and primary sclerosing cholangitis (Peng et al., 1995). Other authors found that administration of ursodeoxycholic acid in patients with primary biliary cirrhosis, who have undergone polypectomy, is connected with vastly reduced risk of CRP relapse (Serfaty et al., 2003).

### **10.5 Selenium**

Abundant data for the role of selenium as a prophylactic substance for the CRC are constantly accumulating. Epidemiological studies have shown anticancer role of selenium since 1970. In some parts of Europe there is low amount of selenium in the soil and European population show tendency of lower intake of selenium in the last 25 years (Rayman, 2000). A lower risk for CRC was detected in persons who take 200 g selenium daily (Clark et al., 1996). Some authors found lower serum levels of selenium in patients with CRC (Scieszka et al., 1997).

We can conclude that the choice of proper chemopreventive tool is difficult. Such a tool must be effective, cheap, safe and easy to use. It is calculated, that up to 80% of the cases with CRC could be prevented by alteration of diet habits (Cummings & Bingham, 1998). These data oblige us to fully clarify the role of chemoprevention in colorectal neoplasms. Combination of chemoprevention with screening endoscopy is of great importance for reduction of the CRC mortality. The most significant chemopreventive agents are the acetylsalicylic acid and other NSAIDs, antioxidants, calcium and selenium.
