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Keratoacanthomas are round, firm, usually flesh-colored nodules with sharply sloping borders and a characteristic central crater containing keratinous material; they usually resolve spontaneously.
Etiology is unknown. Most experts consider these lesions to be well-differentiated squamous cell carcinomas with a tendency to involute.
Development is rapid. Usually the lesion reaches its full size, typically 1 to 3 cm but sometimes > 5 cm, within 1 or 2 mo. Common sites are sun-exposed areas, the face, the forearms, and the dorsum of the hands. Spontaneous involution may start within a few months. However, because this lesion cannot be relied on to involute, biopsy or excision is recommended. Spontaneous involution may leave substantial scarring; surgery or intralesional injections with methotrexate or 5-fluorouracil usually yield better cosmetic results, and excision allows histologic confirmation of the diagnosis.
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