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Squamous Cell Cancer

Presentation. Squamous cell carcinoma (squamous cell cancer) is the second most common skin malignancy after basal cell carcinoma. It appears as a keratotic lesion on sun-exposed skin, including the lower lip. Most squamous cell cancers are slow growing, but larger lesions have a potential for regional lymph node metastasis. This is particularly true for lesions of the lower lip, ear, scalp, and genitalia, which have a 10-30% risk of metastatic spread.

Keratoacanthoma, a subtype of squamous cell cancer, may enlarge to more than a centimeter in a few weeks. This variant rarely metastasizes, but may be locally aggressive.

Etiology. Sun exposure and fair skin type predispose to squamous cell cancer. Squamous cell carcinoma on the hands, feet, or genitalia may be induced by papilloma virus. Previous exposure to ionizing radiation and arsenic are uncommon causes. Aggressive squamous cell cancer may also develop in scars or chronic ulcers. Transplant patients receiving immunosuppressive agents have a 5- to 20-fold increase in the incidence of squamous cell cancer, developing more frequently with the years.

Diagnosis. Squamous cell carcinomas are usually firmly indurated keratotic plaques; they may be ulcerated or have a crater-like center. More subtle squamous cell cancer may look like an irregular erythematous scaling patch, resembling a patch of eczema or dermatophyte infection. squamous cell cancer of the genitals may resemble venereal warts or chronic shallow ulcers. Nonhealing or worsening leg ulcers may indicate development of squamous cell cancer, and adequate tissue is required.

Therapy. Squamous cell carcinoma is treated by excision or destruction. Lesions which are biopsied and proven to be squamous cell carcinoma in situ may be treated.

Squamous cell carcinoma, like BCC, can be locally aggressive, and for extensive lesions, critical areas, or poorly differentiated lesions, Mohs micrographic surgery.

For patients taking immunosuppressant drugs, protection from UV radiation with broad-spectrum sunscreens is important but often overlooked. These patients are at risk for developing squamous cell cancers rapidly; their immune suppressants may allow earlier metastasis and death from an eminently preventable skin lesion.

Diagnostic and therapeutic challenges. As with BCCs, destructive treatment with an inadequate diagnosis can result in recurrence and significant morbidity. Innocuous scaling patches on hands, feet, or genitals can be treated as warts, eczema, or fungal infection and may become extensive or invasive.

Particular attention must be given to scalp, ear, and lip lesions; in these cases, a careful examination of regional lymph nodes is indicated. Failure to monitor and prescribe sun protection for high-risk individuals.