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A precancerous or premalignant lesion is one that has a strong likelihood of transforming into a malignancy. There is much debate about the validity of the concept of precancerous lesions, and the terminology has been confusing.1–4 Lesions discussed in this chapter are those that have a clinically demonstrated potential to become invasive carcinomas and are characterized by histologic atypia confined to the epidermis. The focus is only on the precancerous keratinocyte lesions and not on those of other epithelial cells such as the melanocyte, Merkel, and appendageal cells. Discussion of malignancies and premalignancies associated with these cells can be found in (Chapters 119, 120, and 123) respectively.
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A common feature of all premalignant keratinocyte tumors (Table 113-1) is that they have the potential to become invasive squamous cell carcinoma (SCC). These precancerous lesions and SCC are considered by many to represent a continuum of disease with dysplasia at one end of the spectrum and invasive carcinoma at the other.
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Actinic keratoses (AKs) or solar keratoses are cutaneous neoplasms consisting of proliferations of cytologically abnormal epidermal keratinocytes that develop in response to prolonged exposure to ultraviolet (UV) radiation. The concept of a precancerous keratosis was first presented by Dubreuilh in the late 1800s.5 AKs were first identified and named keratoma senilis by Freudenthal in 1926.6 In 1958, Pinkus further characterized these lesions and coined the term actinic keratosis.7 These lesions have also been called solar keratoses and senile keratoses. Actinic ...