Chemoprevention of nonmelanoma skin cancer.

Chemoprevention is suitable for patients who are at high risk of development of numerous or invasive nonmelanoma skin cancers (NMSCs). Various substances have been studied as potential chemopreventive agents for NMSC. Oral retinoids have been proven to be effective in the suppression of new squamous cell carcinoma (SCC) development. Patients need to stay on oral retinoids as long as chemoprevention is needed with careful monitoring of the dose and side effects. Topical retinoids are not effective in prevention of NMSC. In organ transplant patients with aggressive or numerous skin cancers, decrease in the immunosuppression or switch to mammalian target of rapamycin inhibitors (sirolimus or everolimus) can be considered. Field therapy for areas of severe actinic damage with photodynamic therapy, imiquimod, 5-fluorouracil, ingenol mebutate, or diclofenac sodium may theoretically decrease the risk of SCC through treatment of precancerous changes. However, there is limited data regarding efficacy of these agents in chemoprevention of NMSC. Epidemiologic studies suggest a protective role for nonsteroidal anti-inflammatory agents in development of NMSC. Limited data support chemopreventive effect of difluoromethylornithine and T4 endonuclease V for actinic keratoses and basal cell carcinoma. Amongst dietary factors, low-fat diet, limonene from citrus fruit peel, and caffeine may protect against NMSC. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.