Intervention trials on colorectal cancer prevention.

Epidemiological studies have emphasized the major role played by diet in the etiology of large-bowel cancer. Attempts to identify causative or protective factors in epidemiological and experimental studies have led to some discrepancies. The time has come to test the most important hypotheses within the framework of intervention studies. Of 14 studies specifically devoted to colorectal carcinogenesis, nine have been completed and five are ongoing; all the studies evaluate the effect of the intervention on adenoma recurrence and three studies also examine adenoma growth. In addition, five intervention trials considering cardiovascular diseases and various cancer sites will provide data on the effect of the intervention on colorectal cancer incidence. The interventions being evaluated are supplements of vitamins (with or without other antioxidants), fibre or calcium, as well as dietary modifications. Most available data do not support a protective effect of vitamins and antioxidants on colorectal carcinogenesis. There are some arguments in favour of a protective effect of dietary fibre and/or a low-fat diet on adenoma growth. The results of ongoing studies will be available within two to three years. If one of the evaluated interventions proves effective, it will indicate a simple, safe and inexpensive prophylaxis for a very common cancer.