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INTRODUCTION

Squamous cell carcinoma (SCC) most commonly originates from keratinocytes in sun-damaged skin either de novo or from a preexisting actinic keratosis or SCC in situ (also known as Bowen’s disease), predominantly affecting the head, neck, and arms. It can also arise in nonsun-exposed skin most commonly from chronic leg ulcers and burn scars.

EPIDEMIOLOGY

Incidence: it is the second most common skin cancer in Caucasians and the most common skin cancer in darkly pigmented skin. Approximately 150,000 cases/year are diagnosed in the United States

Age: most common in patients over 55 years

Race: mainly affects Caucasians

Sex: higher incidence in males

Precipitating factors: chronic ultraviolet radiation and fair skin are the most significant predisposing factors. Other factors include immunosuppression, human papilloma virus infection, ionizing radiation, arsenic exposure, genetic disorders (epidermodysplasia verruciformis, albinism, xeroderma pigmentosum, epidermolysis bullosa), PUVA exposure, smoking, and chronic inflammation (ulcers, burn scars, discoid lupus)

PATHOGENESIS

The most common altered gene in SCC is the p53 tumor suppressor gene, resulting in keratinocyte immortalization and unregulated cell proliferation.

PHYSICAL EXAMINATION

Hyperkeratotic skin-colored to erythematous papule, plaque, or nodule (Figs. 53.1 and 53.2). It can be ulcerated, friable, or exophytic. It most commonly presents within sun-damaged skin.

Figure 53.1

Invasive squamous cell carcinoma on the right neck

Figure 53.2

Recurrent squamous cell carcinoma on the chest of an elderly woman

DIFFERENTIAL DIAGNOSES

Keratoacanthoma (Fig. 53.3), hypertrophic actinic keratosis, basal cell carcinoma (BCC), inflamed seborrheic keratosis.

Figure 53.3

Giant keratoacanthoma on the chest. Many authors regard keratoacanthomas as variants of well-differentiated squamous cell carcinoma

LABORATORY DATA

Dermatopathology

Proliferation of atypical keratinocytes with variable differentiation of the epidermis and variably sized nests and islands invading the dermis. Foci of keratinization are noted in well-differentiated variants. Perineural involvement may be observed.

COURSE

SCC tends to be more aggressive than BCC, with a reported 2% to 3% incidence of metastasis. Mucocutaneous SCC has a higher rate of metastasis, as high as 11%. More aggressive forms of SCC are observed in immunosuppressed patients or SCC that arises within previously irradiated sites, scars, burns, and areas of inflammation. There is a higher metastatic potential for SCC arising on the ear and the lip.

KEY CONSULTATIVE QUESTIONS

Evaluate for past history of blistering sunburns and chronic sun exposure. Determine if other predisposing factors are present ...

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