Solid tumours--chemoprevention with retinoids.

There is a clear change in the treatment strategies for solid tumours towards the treatment of early rather than advanced disease. Retinoids represent a potentially useful class of drugs in chemoprevention. Preclinical data and clinical experience suggests that different retinoids may have different spectra of antitumour activity and synergistic interactions between retinoids and cytokines have also been reported. 13-cis retinoic acid has shown some promising activity in preventing the onset of second primary tumours in head and neck cancer and fenretinide is being tested in the prevention of second primary breast cancers. An understanding of the role of the different retinoid receptors could lead to the design of compounds with a better therapeutic index. Despite these early indications that retinoids could be useful in this area, the development of such drugs is far from easy. Appropriate study designs for screening differentiating agents in the clinic, and the relevance of preclinical models of chemoprevention are challenges to be addressed. Unresolved issues include optimal patient selection, long clinical trial times, optimal dose, schedule and treatment duration. The use of biological surrogate markers for longer time-dependent trial endpoints could significantly contribute to more rapid development. Ongoing clinical studies, particularly in tobacco-related diseases, will better define the role of retinoids in this clinical setting. Clinicians should be encouraged to enter patients into large well organized clinical studies.