Cellular Classification of Skin Cancer
SCCs are composed of keratinizing cells. These tumors are more aggressive than BCCs and have a range of growth, invasive, and metastatic potential. Prognosis is associated with the degree of differentiation, and tumor grade is reported as part of the staging system. A four-grade system (G1-G4) is most common, but two- and three-grade systems may also be used. Mutations in the PTCH1 tumor suppressor gene have been reported in SCCs removed from patients with a prior history of multiple BCCs.
SCC in situ (also called Bowen disease) is a noninvasive lesion. It may be difficult to distinguish it pathologically from a benign inflammatory process. The risk of development into invasive SCC is low, reportedly in the 3% to 4% range.
Actinic keratoses are potential precursors of SCC, but the rate of progression is extremely low, and the vast majority do not become SCCs. These typically red, scaly patches usually arise on areas of chronically sun-exposed skin and are likely to be found on the face and dorsal aspects of the hand.
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