Squamous neoplasia (subtypes) and progression

Actinic keratosis (AK), squamous cell carcinoma in situ/Bowen disease (BD), and invasive squamous cell carcinoma (SCC) represent different stages of a disease continuum and are thus summarized under the term squamous neoplasia (SN). In general, all types of squamous neoplasia of the skin derive from epidermal keratinocytes. AK and BD are limited to the epidermis and do not pose a significant risk for the patient. In contrast, invasive SCC has the risk to metastasize with immunosuppressed patients being at special risk. In this regard, treatment of these lesions differs significantly. Whereas invasive SCC requires surgical excision, AK and BD may be treated noninvasively by physical destruction (e.g., cryotherapy or laser) or by application of special topical medications. (Please refer to Chapter 47 for further information of reflectance confocal microscopy [RCM] monitoring.) Patients often present with multiple lesions, thus the identification of early invasive SCC may be difficult. RCM may aid in differentiation and may help to distinguish squamous neoplasia from BCC, as well as from other benign lesions such as seborrheic keratoses.