Epidermal Precancers and Cancers

Cutaneous epithelial cancers (nonmelanoma skin cancer [NMSC]) originate most commonly in the epidermal germinative keratinocytes or adnexal structures. The two principal NMSCs are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). SCC often has its origin in an identifiable in situ lesion that can be treated before frank invasion occurs. In contrast, in situ BCC is not known, but minimally invasive "superficial" BCCs are common.

The most common etiology of NMSC in light-skinned individuals is sunlight (ultraviolet radiation [UVR]), and human papillomavirus (HPV). Solar actinic keratoses are the most common precursor lesions of SCC in situ (SCCIS) and invasive SCC occurring at sites of chronic sun exposure in individuals of northern European heritage (see Section 10). UVR and HPV cause the spectrum of changes ranging from epithelial dysplasia to SCCIS to invasive SCC. Much less commonly, NMSC can be caused by ionizing radiation (arising in sites of chronic radiation damage), chronic inflammation, hydrocarbons (tar), and chronic ingestion of inorganic arsenic; these tumors can be much more aggressive than those associated with UVR or HPV. In the increasing population of immunosuppressed individuals (those with HIV/AIDS disease, solid organ transplant recipients, etc.), UVR- and HPV-induced SCCs are much more common and can be more aggressive.