Chemoprevention of colorectal cancer

Abstract

Colorectal cancer is a major cause of mortality and treatment costs are considerable. Advocating lifestyle modification, faecal occult blood testing and surveillance colonoscopy in appropriate populations are already in practice. A developing concept is chemoprevention. Several models of carcinogenesis in colorectal cancer have been developed and there is an increasing database on the major molecular mechanisms involved in carcinogenesis mainly from preclinical experiments and phase I trials. There have been several large epidemiological and observational studies to evaluate possible protective effects of >200 agents. More recently, case-control and cohort studies and well-conceived, phase II/III clinical trials have been done or are under way to evaluate putative chemopreventive agents including established drugs like aspirin and non-steroidal anti-inflammatory drugs (NSAIDs), 5-aminosalicylates and statins; more controversial drugs like cyclo-oxygenase-2 (COX-2) inhibitors, ursodeoxycholic acid; various vitamins and micronutrients including calcium, selenium, folic acid, and dietary fibre, fat and protein content. Despite promising outcome in preclinical studies, there is currently very limited data from well-controlled and appropriately powered clinical studies. The most promising agents currently are aspirin, traditional NSAIDs and COX-2 inhibitors. The recent reports of cardiovascular risks of the COX-2 inhibitors and some traditional NSAIDs have resulted in stagnation of the field. Pending the expected release of results from several phase III trials in the near future, chemoprevention for colorectal cancer can only be practically considered in the very-high-risk population like those with familial adenomatous polyposis and ulcerative colitis, in conjunction with surveillance colonoscopy. This article reviews the major models of colorectal carcinogenesis, the concept of chemoprevention with special reference to colorectal cancer and the current state of clinical literature and the future direction of colorectal cancer chemoprevention for both researcher and clinician alike.