Chemoprevention can be defined as an attempt at
cancer control in which the occurrence of the disease is prevented by the administration of one (or more) chemical compounds. Main problems in
chemoprevention studies are the choice of a suitable
drug, the choice of an appropriate intermediate or definitive end point, and the definition of the population which should be investigated. Main classes of chemopreventive agents include
vitamins, non-
steroid antinflammatory drugs, minerals such as
calcium or
selenium, and other
antioxidants such as
N-acetylcysteine.
Chemoprevention is particularly appealing in
colorectal cancer, either because these lesions develop through a multistep process, or owing to the concept of "field
carcinogenesis'. Between 1985 and 1990 we carried out a controlled study in which
antioxidant vitamins or
lactulose were used in an attempt to prevent the recurrence of colorectal
polyps after their endoscopic removal. Among the 209 patients who could be evaluated,
polyps recurred in 5.7% of the individuals who were given
vitamins (A, C and E), 14.7% of patients given
lactulose and 35.9% of untreated controls (chi 2 = 17.1, P < 0.001). The study suggested that either
antioxidant vitamins or
lactulose could be effective in reducing the recurrence rate of
adenomatous polyps. In a subsequent on-going study, lower doses of the same
vitamins were tested versus
N-acetylcysteine (600 mg/day) or no treatment. Preliminary results showed a 40% reduction of the recurrence of
polyps (versus controls) in individuals given
N-acetylcysteine, while the effect of lower doses of
vitamins was less appreciable. Definitive results of the study should be available by the end of 1998.