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Rates of squamous cell and basal cell carcinomas have been increasing, possibly as a result of increased exposure to ultraviolet radiation. Primary care physicians can expect to diagnose six to seven cases of basal cell carcinoma and one to two cases of squamous cell carcinoma each year. Basal cell carcinomas may be plaque-like or nodular with a waxy, translucent appearance, often with ulceration and telangiectasia. They rarely metastasize and are treated with excision, cryotherapy, electrodesiccation and cautery, imiquimod, 5-fluorouracil, or photodynamic therapy (the latter is not approved for this purpose by the U.S. Food and Drug Administration) , although surgery results in the fewest recurrences. Actinic keratoses are scaly keratotic patches that often are more easily felt than seen. They are amenable to any of the destructive techniques described above, with the exception of photodynamic therapy. Squamous cell carcinomas arise from keratotic patches and become more nodular and erythematous with growth, sometimes including keratin plugs, horns, or ulceration. Because they may metastasize, they often are treated with excisional biopsy.(Am Fam Physician 2004;70:1481-8. Copyright© 2004 American Academy of Family Physicians.)
The incidence of basal cell and squamous cell carcinomas, which also are called nonmelanoma skin cancer, has been increasing steadily over the past 30 years.1,2 The reasons for this increase appear to be largely sociologic and include increasing amounts of sun exposure and use of artificial tanning beds. Primary care physicians can expect to diagnose six to seven cases of basal cell carcinoma and one to two cases of squamous cell carcinoma each year.3 The major risk factor for the development of skin cancer is exposure to ultraviolet (UV) radiation. In addition, ozone depletion may increase UV radiation exposure and thus increase rates of skin cancer,4,5 but other factors also increase risks (Table 1).
Natural History
Basal cell and squamous cell carcinomas develop within the epidermis (Figure 1). Basal cell carcinomas are derived from the basal layer of keratinocytes, which is the deepest cell layer of the epidermis. Squamous cell carcinomas arise from the more superficial layers of keratinocytes. Keratinocyte damage is a response to repeated exposure to UV radiation, occurring especially in susceptible persons. One study6 found that a single tanning session was enough to damage DNA in keratinocytes. The damage results in...