Results, toxicity and compliance in chemoprevention trials of head and neck cancer.

Several clinical trials have demonstrated the efficacy as chemopreventive agents on upper aerodigestive tract (UADT) cancer of vitamin A or its natural precursor, beta-carotene, or its synthetic analogues, retinoids. Particularly, 13-cis-retinoic acid (cRA) has been shown to reverse oral leukoplakia and to reduce the frequency of second primary tumours in patients treated for head and neck cancer. Since chemopreventive treatments must be of very long-term duration (even years), and because of apparent 'good health' of treated patients, the toxicity of used drugs and the compliance with treatment need to be carefully considered. Current clinical research has evaluated the efficacy of low doses of cRA in larger numbers of patients, and the increased effectiveness of cRA when used in combination with recombinant alpha-interferon 2a (r-alpha-IFN 2a) has also produced high objective response rate in patients affected with squamous cell carcinoma of the head and neck. In vitro and in vivo studies to verify the validity of several biomarkers (in particular micronuclei) as intermediate end-points in chemoprevention studies are continuing, to allow the short-term screening of promising chemopreventive drugs to be used in clinical trials. The published literature on this matter is reviewed, with special attention to retinoid treatment and toxicity/compliance-related problems, and compared with our own experience.