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Cutaneous squamous cell carcinomas (SCCs) are malignant neoplasms derived from suprabasal epidermal keratinocytes. These and basal cell cancers are the nonmelanoma skin cancers that represent the most common malignancies in humans. Whereas basal cell carcinoma (BCC) (see Chapter 115) is thought to arise de novo, SCC probably evolves in most cases from precursor lesions of actinic keratosis (AK) and Bowen disease (SCC in situ) (see Chapter 113). This chapter focuses on clinical aspects of invasive SCC. Cutaneous SCC represents a broad spectrum of disease ranging from easily managed, superficially invasive cancers to highly infiltrative, metastasizing tumors that can result in death. The clinical presentation can be variable despite the existence of easily identified typical lesions. The cellular and molecular aspects of SCC carcinogenesis are discussed elsewhere (see Chapter 113).
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The precise incidence of BCC and SCC is unknown, because these cutaneous malignancies are not generally documented by the National Cancer Institute or most state cancer registries. However, it is generally accepted that well over 1 million cases are diagnosed in the United States each year, with approximately 200,000 representing SCC.10 Although less common than BCC, SCC carries a risk of metastasis and thus accounts for the majority of the several thousand deaths attributable to nonmelanoma skin cancer each year. By comparison, cutaneous melanoma accounts for only 60,000 cases, but approximately 9,000 deaths, annually.11 Similar trends for SCC have been noted in Australia12 and the Caribbean.13
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SCC is strongly associated with advanced age, and a sharp increase in incidence is seen after age 40 years.14 Today, the lifetime risk of SCC among whites is approximately 15%, almost double that of two decades ago. Increased exposures to ultraviolet (UV) radiation (through greater use of tanning salons, increased time spent outdoors, changes in clothing styles, and ozone depletion) and greater longevity have been suggested as possible causes for the increase in disease. It is likely that this trend will continue as a result of further depletion of the ozone layer and the aging of the US population. The rising incidence of SCC over the past several decades has been paralleled by a 20% decrease in mortality, attributed largely to increased public awareness and aggressive treatment of high-risk lesions.15 After a diagnosis of SCC, patients have a 44%–50% cumulative risk of developing another nonmelanoma skin cancer (18%–30% risk of SCC) in the subsequent 3–5 years.16 In addition, these patients are at increased risk for extracutaneous–cancers.17
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Squamous cell cancer is twice as common in men as in women, probably ...