Keratoacanthoma is a round, firm, usually flesh-colored nodule with sharply sloping borders and a characteristic central crater containing keratinous material; it usually resolves spontaneously.
Etiology is unknown. Most 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 may be > 5 cm, within 1 or 2 mo. Common sites are sun-exposed areas, the face, the forearm, and the dorsum of the hand. Spontaneous involution may start within a few months. However, because this lesion cannot be relied upon 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.
Last full review/revision September 2008 by Daniel W. Collison, MD
Content last modified February 2012