Figure 2.

Schematic representation of processes involved in ultraviolet (UV) radiation-mediated development of skin cancer, and examples of chemopreventive agents reported to be useful at different stages of the carcinogenic process. Normally, when skin is exposed to UV radiation, it initiates tumor formation by DNA damage, mutagenesis and release of reactive oxygen species. After damage to the cells, the initiated cells with mutations inferring greater growth potential expand to become pre-neoplastic lesions. If these lesions are not found and removed, they may progress through transformation and become malignant skin cancers and require treatment, which is not always successful (as indicated by the dashed up arrow). Additionally, many melanomas reoccur after successful treatment (dashed down arrow). Chemopreventive agents can be applied topically that directly block the UV rays from reaching to the skin, or can be used to reverse or delay the process of multi-stage carcinogenesis at one or at all of the stages, depending on their efficacy. The ideal chemoprevention regimen would target all stages of cancer development and may include a combination of two or more agents in order to obtain the greatest preventive effects against UV-induced melanoma.