Cancer precursors.

A significant proportion of cutaneous malignancies arise from well-defined precursor lesions that have often been present for many years. This provides an opportunity to reduce rates of skin cancer by recognition and treatment of these lesions. Precursors of keratinocytic malignancy, such as actinic keratoses and Bowen's disease, are extremely common in the older, white population and will frequently be encountered by generalist physicians in the context of examinations for noncutaneous conditions. Less common conditions, such as erythroplasia of Queyrat and nevus sebaceous, are associated with a higher risk of malignant change, and their recognition is therefore imperative. The management of the various precursors of melanoma remains controversial, as the exact risk of malignant transformation of many of these lesions is still unclear.