Chemoprevention of colorectal cancer.

Colorectal cancer is the fourth commonest form of cancer in men with 678 000 estimated new cases per year worldwide, representing 8.9% of all new cancers. The disease is most frequent in Occidental countries and particularly so in North America, Australia, New Zealand, and parts of Europe. Prospects for colorectal cancer control are bright and a number of possible approaches could prove fruitful. Among these, pharmaceutical measures seem to be valid and logical approaches to the prevention of colorectal cancer and diminishing its impact. Such approaches could concentrate in primary prevention in at-risk subjects or be applied in altering the course of precursor or established disease. Treatments used must fulfil basic requirements of biological plausibility and safety in continued use in large numbers of subjects. Those available include vitamins and minerals, and other drugs with potential as antioxidants, immune modulators or promoters of cell differentiation or apoptosis. Of the various regimens suggested, vitamin A supplementation may even predispose to adverse outcomes, and antioxidant vitamins in general have no coherent body of evidence to support their use. N-acetylcysteine and ursodeoxycholic acid have promising characteristics but there are as yet no clinical data to support the use of the former in gut epithelial cancer, and formal dose ranging studies must be carried out before the latter is submitted to large scale trial. Folate shows promising characteristics but non-steroidal anti-inflammatory drugs and vitamin D seem the most promising agents. Both seem to reduce the incidence of disease, and to reduce growth rates and/or induce differentiation or apoptosis in gut epithelial cancer cells. Both are also well understood pharmacologically. They may be preferred to newer selective compounds in the same class until these newer compounds are confirmed as safe for widespread long term use.