Squamous cell carcinoma (SCC) is a form of skin cancer that originates from epithelial keratinocytes.1 It is thought to arise as a focal intra-epidermal proliferation from precancerous lesions, including actinic keratoses, SCC in situ, Bowen's disease, bowenoid papulosis, erythroplasia of Queyrat and arsenical keratoses.2 Without treatment, SCC may continue to grow, invade the dermis or subcutaneous tissues or metastasise.3 This chapter focuses on interventions for localised, non-metastatic invasive SCC. The prevention of SCC is dealt with in Chapter 22.
Rochester Epidemiology Project in the US estimated the overall incidence of invasive SCC to be 106 per 100 000 people.5 However, several population-based studies have shown that the risk of SCC appears to correlate with geographic latitude. The reported incidence of SCC is higher in tropical regions than in temperate climates, with an annual incidence approaching 1:100 in Australia.6-9 Regional differences related to latitude have also been noted in the US.4,10-13
Sunlight exposure is an established independent risk factor for the development of SCC. SCC arises more commonly in the sun-exposed areas, including the head, neck and arms, but also occurs on the buttocks, genitals and perineum.14 Other risk factors for SCC include older age, male sex, Celtic ancestry, increased sensitivity to sun exposure, increased number of precancerous lesions and immunosuppression.4,15,16 Exposure to oral psoralens, arsenic, cigarette smoking, coal-tar products, UVA photochemotherapy and human papilloma virus have been associated with SCC. Genetic disorders that predispose to SCC include epidermodysplasia verruciformis, albinism and xeroderma pigmentosum.
Stasis ulcers, osteomyelitic sinuses, scarring processes such as lupus vulgaris, and vitiligo have been reported to increase the risk of SCC, but it is unclear how far the morphology of the underlying process delays the diagnosis.15,16
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